The experimental results which we had conducted in the past were synthesized to find universal characteristics of disk flutter which is commonly seen in various drive structures and internal gas conditions. Disk flutter vibrations in 3.5” and 2.5” hard drives equipped with different types of flow mitigation devices were measured under the various mixture ratios of internal helium-air mixture gas and disk speeds. It was found that the amplitudes of disk flutter vibrations showed the same trend with respect to the product of gas density and disk speed: At low gas densities and disk speeds, the vibration amplitudes were quite small. At high densities and speeds, they were large, and their variations were small. In the middle, meanwhile, they showed large amplitudes and variations. In conclusion, it looks to be associated with laminar and turbulent flow regimes. To explain the experimental results by Reynolds number, the characteristic length must take the similar values in the 3.5” and 2.5” drives, but the suitable one has not been found yet.

We propose pivot-to-enclosure fastening improvements to reduce torsional vibration of coil in hard disk drive. The concept is decoupling the coil torsion mode from the actuator’s main resonance mode by reducing the differences in coefficient of thermal expansion between the base boss shaft and the pivot shaft, so as to suppress axial force relief in the pivot screw at 60 degrees C. Based on this concept, three approaches to pivot-to-enclosure fastening improvements were considered: 1. Long pivot screw, 2. SUS stud press fit, 3. Shaft threaded. The axial force reliefs in pivot shaft due to high temperatures were calculated for these three cases, and it was confirmed that the axial force reliefs were suppressed in all cases. The coil torsion mode gain in the frequency response functions was also reduced. Furthermore, a correlation between the coil torsion mode gains and the frequency separations from the coil torsion mode to the main resonance mode was found. Therefore, it is considered that decoupling of coil torsion mode from main resonance mode is one of key factors in coil torsion gain reduction.

Iterative learning control is effective to improve responses of systems that operate repeatedly. Iterative learning control generates feedforward control to reduce errors in the operation, revising the feedforward control using the errors in the previous operation. Iterative learning control may start in the middle of the operation to reduce memory usage. The time to iterative learning control starts are different when iterative learning control starts in the middle of the operation, and those time differences make iterative learning control less effective. In this paper we propose a new method that revise output of iterative learning control for the time differences to start iterative learning control. The proposed method shifts the output of iterative learning control in time because the time differences to start iterative learning control cause time deviations between the output of systems and iterative learning control. Simulation results show that the proposed method is effective and reduces the influence of the time differences to start iterative learning control.

Many factories and power stations lack piping working drawings, thus leading to the demand for 3D models. To address this issue, we are motivated to develop a piping measurement device deployed SLAM algorithm with an RGB-D camera and a motor. One method for reducing the computation cost of SLAM is low frame rate (LFR) processing. To evaluate the impact on SLAM performance with LFR input, we conducted a set of experiments with indoor high-altitude mounted pipes. The results indicate that the feature-based RGB-D SLAM is not affected significantly by LFR input in experimental piping scenes.

In preceding research work made by scientists, the fluid flow driven by stacked corotating disks inside a container such as hard disk drive (HDD) for information storage device is known to be complicated, highly unsteady, and three-dimensional. During the measurement by particle image velocimetry (PIV) concept, we have discussed the results obtained and analyzed in the orthogonal coordinate system for the rotating flow which was transformed into the cylindrical coordinate system. In this study, we apply refractive index matching (RIM) to a simplified HDD model, perform flow visualization and PIV measurements in different insertion angle of the read and write arm (RWA). Behavior of this flow fields are then studied and reported at all areas visible during the experiment. The particle images in the orthogonal coordinate system are mapped to the cylindrical coordinate system, the PIV analysis is directly promoted in the cylindrical coordinate system, the velocity distribution and vorticity are calculated, and the comparison with the conventional method is verified.

Three-dimensional measurements of fluid flow using astigmatism often use microscopes in micro-scaled flows. However, three-dimensional flow measurement is necessary not only for the micro scale under microscopic observation, but also for relatively large scales. In this study, we focus on three-dimensional unsteady rotating flow driven by corotating disks in an enclosure for the purpose of observing complex fluid flow in a hard disk drive. In visualization experiments, three-dimensional particle tracking is achieved by geometric perspective based on simple size of particle image and astigmatism based on the aspect ratio or difference between vertical axis and horizontal axis of individual particle images by using cylindrical lens in the depth direction, and by in-plane position of particle image. In calibration experiments, calibration line was obtained by traversing particles on a horizontal stage. As a result, geometric perspective effect was more dominant than astigmatism effect in the depth direction. The effective area which displays relatively clear particle image in the plane of the measurement domain was also estimated. In the presentation, the performance of this method will be evaluated and its application to complex rotating flows in a container will be reported.

Decreasing head/medium spacing and Heat-Assisted Magnetic Recording (HAMR) are key issues for achieving future high density hard disk system. Single graphene (SG) film is the most promising material for those technologies because of monomolecular thickness around 0.3 nm, large heat resistance for FePt magnetic recording medium (850K, Curie temperature) and high shield performance against migration of Co or Fe ions which causes creation of smear. However, single crystal graphene film is basically inert with weak bonding to substrate and lubricant. In this report, we examined new lubricants, perfluorinated poly ether (PFPE) with OH and phenyl groups for some graphene materials, i.e. single crystal graphene, graphene oxides (GO), or SG film on CoPt using surface-enhanced Raman spectroscopy (SERS) with new optical device, i.e. transmission-type plasmonic sensor. The lubricant exhibits good bonding performance to defect structures in graphene oxide through phenyl groups, Defect structures are composed of dangling bonds or oxidated carbon. Thermal resistance of the lubricant on GO increases compared with non-bonding lubricant on SiO₂. According to the depth profile of Raman spectra around interface between SG film/CoPt medium, the SG film adheres to the CoPt medium through Co hydroxide.

In recent years, the demand for hard disk drives (HDD) has been growing in the midst of a huge amount of information handled with the development of AI and deep-learning. In particular, a demand for HDD for data centers is growing, and capacity of HDD is required. Currently, there is concern that diamond-like carbon (DLC) overcoats will be destroyed by high temperatures in thermally-assisted magnetic recording (HAMR). To solve this problem, we considered using graphene as a protective layer. In this study, we investigated the adsorption amount and surface structure of lubricants on DLC, graphene, UV-treated graphene, and heat-treated graphene using ellipsometer and Raman spectroscopy. We also investigated the heat resistance of graphene. As a result, it was found that UV treatment and heat treatment of graphene increased the amount of lubricant adsorption. We also found that the heat resistance of graphene changes greatly depending on whether it is UV treated or not.

Tribological technology is undergoing a major transition with the development of electrical technology, and electrical bearing failures are frequently reported, especially in EVs. This is a problem that limits the service life of not only EVs but also other mechanical products that use electric motors. The cause is thought to be poor lubrication due to electric current. In this study, polyphenylethers, which has excellent properties even under severe conditions, were used as a lubricant. The tribofilms were found to be more easily formed on the contact surface which was connected to a positive electrode. Based on the analysis of ToF-SIMS, the tribofilms mainly consisted of hydrocarbons and graphite-like components. Moreover, components of tribofilm seem to be independent of the applied electric current. It was considered that the chemical component of the tribofilm affected friction coefficient while the adhesion of the tribofilm related to wear.

Using molecular dynamics with our developed reactive force field, we investigated the effect of water on the mechanochemical reaction of nanometer-thick perfluoropolyether D-4OH films at the head–disk interface of heat-assisted magnetic recording. Three types of reactions were observed: hydrolysis, end group–end group association (EEA) reaction, and end group–main chain association (EMA) reaction. The simulation results showed that water molecules accelerate the decomposition of D-4OH and such effect is more noticeable at low pressures than at high pressures. The presence of water induces hydrolysis and accelerates the EEA reaction, whereas the EMA reaction is greatly accelerated by pressure rather than water.

In this study, the elastic modulus, one of the mechanical properties of magnetic heads and disks, was measured using an Ar gas cluster ion beam (Ar-GCIB). The measured elastic moduli were used to estimate the contact between head and disk surfaces using the Hertzian contact model, and the critical contact loads at which head wear occurs were estimated from that model. As a result, it was estimated that head wear occurs when the contact load between the head and disk exceeds 60 to 110 μN for the actual HDIs.

In this study, the possibility of suppressing electrical discharges inside ball bearings was investigated by reducing the resistance between the inner and outer rings by conductive grease between the shield and additional shim plate of the bearing. As a result, it was concluded that the structure proposed in this study can suppress discharge inside the bearing. This type of conductive bearing structure is considered to be more advantageous in suppressing electrical discharges than a bearing with conductive grease sealed inside the bearing.

To explore the relationship between the deformation of the rubber roller and sheet transport velocity, the deformation of the surface of the rubber roller was measured by using optical coherence tomography (OCT), and the effect of the deformation on the sheet transport velocity was studied based on the measurement results. Measurement results showed that the deformation of the surface of the rubber roller was different when the sheet was transported and when it was not, and the surface of the rubber roller in the nip section was first compressed and then extended in the case of sheet transportation. The variation of the deformation is considered caused by the incompressibility of the rubber. It is considered that the sheet transport velocity was influenced by this variation of the deformation of the surface of the rubber roller.

A formulation that predicts a lateral belt motion in a two-cylindrical roller system with a misalignment was proposed. The formulation was established based on the principle that a lateral belt motion stays in equilibrium where the stream of a belt becomes perpendicular to the axis of the downstream, which we clarified in the previous study, and the misalignment angle. We also observed that, in a two-cylindrical roller system, a mechanism that the effect of alignment is equally distributed between the tension and slack sides of the belt during the belt begins to move and travels halfway around the system exists. The mechanism also was considered in proposed formulation. The results using the formulation proposed here are in good agreement with the experimental results.

A roll-to-roll web handling system to transport the web typically comprises an unwind/rewind roller, guide rollers, drive rollers coupled onto servo motors, and a processing part. In the system, web tension and conveying speed controls play an important role in improving product quality. On the other hand, web wrinkles caused by misalignment become a problem because many guide rollers are used in the system. This paper demonstrates a feasibility study of web wrinkle detection based on image processing and deep learning during web transportation in web handling systems. The prototype used in this study can generate arbitrary misalignment between rollers by connecting a drive unit to a guide roller. The camera is used to capture the wrinkles on the web. The web wrinkles are detected using a convolutional neural network based on the captured image. The validity of the proposed approach has been verified by conducting the experiments using the prototype.

The web is a continuous thin film material, is mass-produced by roll-to-roll (R2R) production method. R2R conveys the web by many rolls, but problems such as troughs and creases occur. In addition, when the heat treatment process is included, the internal temperature changes greatly, and wrinkles may occur due to the shrinkage of the web. Hashimoto et al. established a wrinkle prediction theoretical model assuming steady state, but thermal stress was not considered. Therefore, in this paper, for the purpose of confirming the cause and position of wrinkles caused by heating, we conducted wrinkle generation experiments during heating and transportation, and clarified the improvement policy of the prediction model.

W A long, thin, continuous, flexible medium are commonly referred to as a web. Webs are often used as substrates in high-performance flexible devices. Roll-to-roll printed electronics production is expected to be the production method for these devices. However, there are still many problems. If the winding conditions are inappropriate, winding defects such as abrasions can occur. Slippage causes abrasion of the web, which damages the printed material. When the web is scratched, it loses its product value as well as other winding defects. In this study, the effects of winding speed and tension on the occurrence of slippage were investigated by varying the tension and speed in three steps. The modified Hakiel model proposed by Hashimoto et al. was used to compare the relationship between radial stress, interlayer air entrainment, interlayer frictional force and slip in the rolls with misalignment. As a result, it was confirmed that the amount of misalignment was the largest under the winding condition where the radial stress was the lowest. The amount of air entrainment increases under the condition of low internal stress. It is thought that the amount of misalignment increases because the frictional force between the web layers decreases.

This study aims to utilize SMA actuators as a sound source and to investigate the optimal driving method. Heated periodically by AC voltage with appropriate DC bias, the SMA actuator can vibrate and generates sound. In this paper, we investigated the relationship between the amplitude of input signals to the SMA actuator and generated sound. Based on the results of this experiment, we developed mathematical models to represent the input-output relationship of the SMA actuator. Using these models, we successfully flatten the frequency response of the SMA actuator to white noise.

We propose a measurement technique for visualization of thermal distribution on a heated surface in three-dimensional (3D). Our proposed method integrates temperature-sensitive paint (TSP) and phase-shift profilometry that use structured light. Compared to previous thermal measurements, TSP can provide full field measurements. On the other hands, phase-shift profilometry using structured light can provide non-contact measurements. To validate the proposed method, 3D temperature distributions on a hemisphere were measured. Then, we measured the temperature distributions of the hemisphere under localized cooling. 3D thermal measurement technique that uses TSP and phase-shift profilometry is useful method for investigating the temperature distribution on 3D structure’s surface.

Rubber rollers are used in various film production processes due to their high elasticity. Among them, silicone rubber excels in heat resistance and detachability and is also used as a film-forming nip roll, taking advantage of these characteristics. However, it is extremely difficult to control the surface roughness of rubber compared to steel rollers, and the unevenness and light characteristics (transmittance) of the rubber are greatly changed by the transfer. Therefore, in this study, film formation experiments were carried out with the aim of clarifying the transfer phenomenon from the silicone rubber roller to the film formation film. Then, the transfer rate to the film was analyzed from the results of measuring the roughness of the silicone rubber surface and the film surface.

Recently, microphysiological systems (MPS) have attracted attention as an alternative to animal experiments for drug evaluation in drug development. We have developed an on-chip pump-type MPS with an integrated stirrer-based micropump to improve the operability of the MPS, however, instability of flow rate and flow direction has been a problem. In this study, we aimed to improve the pumping capability of the stirrer-based micropump by investigating the shape of the pump chamber and the height of the flow path. In the evaluation, microbeads were introduced into the MPS and the flow rate was calculated from the behavior of the microbeads using particle image velocimetry (PIV). As a result, it was confirmed that the flow direction was defined and the flow rate increased. These results suggest that changing the shape of the flow path of the on-chip pump type MPS can improve the pumping function.

In this paper, we propose a photothermally actuated micropump using a SU-8/Cu composite. The composite is mixure of a photoresist SU-8 and copper particles. The copper particles have photothermal effect induced by the light irradiance. This effect was utilized for the thermo-pneumatic actuation in the proposed micropump. The micropump was composed of a chamber, heater, reservoir, inlet, and outlet. The photothermally actuated heater was fabricated by photolithography of the composite. The other parts were fabricated using softlithography of polydimethylsiloxane. A maximum pumping volume and pressure of the fabricated micropump were 2.52 μL and 329 Pa at 15.4 W/cm² of irradiance, respectively.

In the IoT society, the number of sensor nodes is exponentially increasing. Energy Harvesting (EH) is attracting attention as a method of supplying power to sensors. There has been much studies on vibration EH (VEH) that generates electricity from the movement of the human body. The large device size and complex mechanism of the most of the conventional VEHs for human motion cause discomfort. Regarding these demerits, we have proposed a small and simple cantilever-type piezoelectric VEH (PVEH). The purpose of this study is to establish a design method for the PVEH that can generate power from impulse excitation. The power generation characteristics of the PVEH under impulse excitation were evaluated with different weight of mass. Experimental results showed that the amount of power increased with weight of the mass under constant vibration acceleration. On the other hand, the damping of the generated current waveform was more slowly with increasing the weight. Therefore, the power generation performance of the PVEH is maximized by setting the damping factor to match the generating frequency of impulse excitation.

In the non-orthogonal Lloyd’s mirror interferometer based on the laser interference lithography, the pitch of interference fringe pattern is controlled by adjusting the angle between the exposure substrate and the collimated laser beam projected onto the substrate surface. However, It has been a time-consuming task to adjust the fringe pitch through the iterative process of pattern exposure and development. In this paper, a new method for the "in-situ" evaluation of the pitch of a interference fringe pattern is proposed. Two laser beams having different wavelengths are employed, and are aligned to be coaxial so that the two interference fringe patterns with different pitches can be generated; one interference fringe is employed for the pattern exposure in lithography process, while the other is employed for observing the fringe pitch. An optical system with an one-axis Lloyd’s mirror interferometer and an imaging system placed on the backside of the exposure substrate is developed, and some experiments are carried out to verify the feasibility of the proposed method.

An optical setup for measurement of the pitch deviation of a scale grating based on a new measurement principle is designed and developed in this paper. In the setup, a pair of laser autocollimation unit is employed for detecting the changes in angles of diffraction of the positive and negative first order diffracted beam. Through the arithmetic operation with the obtained information of the changes in angles of diffraction of the positive and negative first-order diffracted beams, the influences of the angular error motion and the local slope of a scale under measurement can be cancelled. Basic performances of the developed optical setup are evaluated in experiments. In addition, the developed setup is applied for evaluating a scale grating with a nominal pitch of 1.6 μm.

Optical angle sensors based on the laser autocollimation method can improve the sensitivity of angle detection by applying a photodiode as the detector. On the other hand, the resolution is affected by the angle detection sensitivity and noise components in the sensor output. In this paper, aiming to improve the measurement resolution of an optical angle sensor based on the laser autocollimation, an attempt is made to reduce the noise components in the readout signals from the photodiode in the angle sensor by directly mounting the detector on a signal processing circuit. Experiments are carried out to verify the feasibility of the developed optical setup.

Convective heat transfer is an important process for many industries and products including electronics, automobiles, and production equipment. Especially the demand for improved cooling capacity is increasing due to the miniaturization of electronic device and the increase in heat generation density caused by the higher density of semiconductors. This requires an improvement in heat transport efficiency. The heat transport efficiency is expected to be improved by micro-particles dispersed in cooling liquid. Although the effects of particle concentration and material are frequently reported, further investigation of fluid and particle behavior with established wall temperature conditions is necessary. In this research, a single-sided heated channel with transparent glass wall with electrically conductive film was created, and the velocity distribution in the channel was measured by micro-PIV using a fluorescence microscope at each temperature conditions. When the bottom surface was heated, convection with complex S-shaped velocity distribution was observed in the channel span direction, which increased with temperature rise. Possible causes are discussed including thermophoresis, Rayleigh-Bénard convection, Marangoni convection, and viscosity coefficient change due to temperature.

With the development of microfabrication and surface treatment technologies, the gaps between elements in mechanical and electronic components have narrowed from the micrometer to the nanometer-sized. Fluid slippage at the solid/liquid interface is one of the phenomena that are considered to occur in micro/nanometer-sized gaps, and frictional properties there are expected to be different from those in macro gaps. For proper lubrication design in nanometer-sized gap, it is necessary to quantify the slippage at the interface. In this study, we used the fluorescence tracking of quantum dots with diameters of a few nanometers to measure the squeezed flow in nanometer-sized gap. Quantitative lateral velocity distributions were measured, and we estimated the slippage based on our proposed analysis of the number distribution of measured velocity values that depends on the flow profile in the depth direction. Our obtained results suggested that interfacial slippage occurred in the gap about less than 200 nm.

Polymer additives in lubrication oils are known to play a role as viscosity index improvers that change the temperature dependence of viscosity. On the other hand, it is assumed that polymers adsorbed on surfaces contribute to low friction, and clarification of their mechanical properties and temperature dependence is essential for lubrication design. In our previous research, we have successfully measured the gap dependence of mechanical properties (shear viscoelasticity) of base oils by applying the fiber wobbling method (FWM), a nano-rheological measurement method that we originally developed. In this study, we developed a temperature-control stage for FWM to measure the temperature dependence of shear viscoelasticity in nano-gaps of polymer-added lubricants.

Antifouling surfaces are required for medical equipment, food containers, and exterior walls. In order to realize the antifouling surfaces, it is necessary to improve droplet sliding efficiency. In this study, we measured the interfacial resistance and sliding velocity of a droplet on the slope of a silicone film. A contact angle measuring device (First Ten Angstroms, Inc: FTA1000) was used. The interfacial resistance was proportional to the power of the sliding velocity. The effect of viscous force on interfacial resistance was smaller than that of surface tension. To consider the relationship between surface tension and viscous force, we calculated the Laplace pressure of the droplet, which is dependent on the droplet shape. Laplace pressure was positively correlated with viscous force, which suggests that droplet shape is determined by surface tension and viscous force.

The slipperiness of the droplet is important for removing the droplet from various solid surfaces. The slippery surface can be used for products and structures that require antifouling and waterproofing. In order to develop a highly slippery surface, it is necessary to predict the sliding behavior of droplets. This study focused on the relationship between the sliding behavior of water droplets on an inclined solid surface and interfacial resistance in order to investigate the behavior of water droplets after they began to slide. Water droplets of various volumes were dropped onto a solid surface and their sliding velocity, contact angle, and width of solid-liquid interface were measured. As a result, it was suggested that the water droplet accelerated at the beginning of the slide and then slide at a constant velocity. When the interface resistance at that time was calculated, it almost matched the gravity component. Furthermore, it was shown that the width of the water droplet solid-liquid interface changes with the sliding velocity. Among the factors related to interface resistance, it was found that the contact angle hysteresis was affected by the volume of water droplets and the tilt angle of the solid surface, and the width of the solid-liquid interface was affected by volume of water droplets.

A micro-meter-sized droplet called satellite droplet can be generated with capillary bridge breakup method. The droplet spontaneously oscillates in an axisymmetric oblate-prolate shape due to surface tension as the restoring force. The oscillation is damped by viscous effects, and the droplet eventually becomes spherical. The period and decay time of the oscillation can be related surface tension and viscosity of a liquid, respectively. Applying these relations, we have developed a new method to measure liquid properties under contactless environment. In this study, satellite droplet oscillations are detected by a photodetector to obtain the period and decay time. At the same time, a single image of the droplet settled in a spherical shape is captured using a CMOS camera to obtain droplet radius. Based on these data, we determined the surface tension and viscosity of liquids and evaluated the accuracy of the measurement. As a result, we obtained both surface tension and viscosity values close to the literature values using distilled water, octane, tetradecane, and hexadecane as a test liquid.

To elucidate the cause of increase in shear resistance in alignment process for nano imprint lithography (NIL), by using vertical-objective-type ellipsometric microscopy (VEM) combined with a micro-cylinder structure and gap feedback-control, shear response of nano-confined liquid film mimicking a NIL resist film were measured. The three kinds of samples were prepared; monomer, monomer with release agent, and monomer with polymerization initiator. The increase in the shear resistance force was not detected with the monomer alone, but with the addition of additives. The shear response waveforms indicated that the resist solidifies at nanometer gaps and may melt above the yield shear force. These results suggest that the additive is unevenly distributed near the sliding solid surfaces and changes the physical properties of the monomer near the solid surfaces, resulting in a significant increase in shear resistance force at the nano gaps. This mechanism is thought to be responsible for the increased shear resistance force in the NIL alignment process as well.

Reducing lubricant viscosity is one effective way to improve the energy efficiency of automobiles. Designing a lubricant with the desired properties requires elucidating the relation between viscosity and molecule structure. In this study, we measured the temperature dependence of dielectric relaxation for lubricants with different molecular structures. The dielectric relaxation measurements can evaluate the motility of single molecules influenced by the ambient viscosity. Additionally, we measured the temperature dependence of lubricant viscosity with a rotational viscometer. By comparing the results of both flow viscosity and dielectric relaxation measurements, we find a correlation between flow activation energy and single-molecule mobility when viscosity is dependent on molecular weight, while there is no correlation between them when polarity dominantly affects viscosity.

The number of people requiring nursing care is expected to increase significantly in the future. However, the number of nursing care workers is not keeping pace with this increase. If the sleep state of those requiring nursing care can be easily estimated, it will be effective in reducing the burden on nursing care workers. We have already developed a method to measure respiration, heartbeat, and body movement of a healthy subject using a flexible tactile sensor sheet by frequency analysis of measured body pressure time series data. In this study, we measured those pieces of biological information of hospitalized patients throughout a night. In addition, we confirmed that the measured biological information can be used to estimate the sleep state.

Monitoring of body and bladder water content can help prevent diseases and incontinence caused by water deficiency. Current methods for measuring body water content are not suitable for use in daily life. In this study, we propose a method using the phase difference of transmitted radio waves. Radio waves in a material have a characteristic that the propagation speed changes depending on the frequency and the electrical properties of the material. As a basic experiment, radio waves of different frequencies were irradiated while increasing the amount of water, and the changes in the phase difference of the transmitted radio waves were measured. This technique can capture changes in water content based on the difference in phase difference due to frequency, and is expected to be used for non-contact measurement over long periods of time in daily life.

The purpose of this study is to propose a non-contact method of measuring arterial blood oxygen saturation and to evaluate the system. In this presentation, a camera was used to measure arterial blood oxygen saturation in a non-contact manner. In order to realize stable measurement, we investigated a method of using a cold mirror (a mirror that reflects visible light and transmits infrared light) to measure the light after spectroscopy with a camera. We believe that the use of a cold mirror for spectroscopy of infrared and visible light will increase the sensitivity of the sensor and reduce noise, and we report on the design, prototyping, and measurement experiments of the device.

A new method of movement in Virtual Reality (VR) is redirected walking (RDW), which is implemented by manipulating the magnification of movement in VR in relation to the same movement in reality, such as taking two steps forward in the VR space when one step forward is taken in reality. RDW is implemented by manipulating the user's viewpoint in VR according to the magnification of the movement. However, if the manipulation is perceived, it causes discomfort. Therefore, the amount of manipulation of RDW is limited based on the user's perception threshold. Although RDW thresholds have been studied in previous research works, they might fluctuate depending on the cognitive load caused by different tasks in VR. Because tasks are rarely performed by walking alone in VR, RDW must be designed by considering the cognitive load in dual tasks. Therefore, in this study, we used a visual search task, which is an important task for humans, as a secondary task to quantitatively evaluate the relationship between the cognitive load (memory load and visual load) and the perceptual threshold in the visual search task, and to study the effect of cognitive load on the perception of RDW. The experimental results showed that the perceptual threshold of RDW increased when the memory load was increased. However, no change in the perceptual threshold of RDW was observed when the visual load was increased. This suggests that the memory load dominates the effect of visual search tasks on RDW and that the increased memory load increases the perceived threshold of RDW. In addition, the method of exploration can affect the perception of RDW because vestibular, visual, and somatosensory information differ depending on the way the body is moved during the visual exploration task.

In daily life, scenarios of skin contact with liquids have become increasingly diverse, and liquids having various properties are being handled. Therefore, many studies have reported the influence of liquid properties on human sensibility. Many studies have been conducted on the influence of the rheological properties of liquids, which affect tactile sensation during application, using sensory indices based on questionnaires. In this study, the influence of the rheological properties of liquids on the tactile sensibility was investigated in terms of the cerebral blood flow and electrocardiographic bioindicators. The results of the study showed significant differences in the cerebral blood flow depending on the conditions. Furthermore, the results of the correlation analysis between the questionnaire and biological information suggested the possibility of using biological information to evaluate the comfort of liquid applications.

The purpose of this study is to establish a technique for estimating sounds heard by humans from brain images captured by fMRI using deep learning. In our previous report, we found that CNN, a type of deep learning, can estimate the pitch of single tones in pure tones and specific tones in chords. On the other hand, sounds we hear in our daily lives are compound waves containing multiple frequencies, and their timbre is determined by their frequency spectrum. Therefore, we suppose it would be possible to estimate the timbre using the same method as in the previous report. In this report, we focused on the relationship between the sound pressure levels of each harmonic in the frequency spectrum and used 3DCNN to estimate the timbre of the musical instrument heard by each volunteer from brain activation images obtained when hearing to two different musical instruments. As a result, the accuracy of the estimation was not sufficient.

Vibration discrimination studies of high frequency in modulated waves have shown that the 125 Hz envelope is not perceivable when humans are presented with a 125 Hz envelope and a 300 Hz or 400 Hz carrier wave. However, the spectrum with two peaks obtained by measuring the actual texture has a smaller peak at higher frequencies. So, the frequency response is not like a modulated wave, and the effect of cutting off the high frequency wave is not known. Therefore, we studied the effect of cutting off high frequency waves in order to reduce the number of peaks to be reproduced in the measurement base. First, we prepared a composite waveform consisting of two sinusoidal waves with different amplitudes and frequencies. Then, subjects evaluated the similarity of vibrations after and before cutting off a high frequency wave by the Visual analog scale. As a result, we found that differences in frequency have a strong influence.

It is important to evaluate the mechanical characteristics of the fingertip, which is one of the factors affecting the tactile sensation. In this paper, to elucidate the relationship between perception characteristics of the roughness feeling and mechanical characteristics of the fingertip with different moisture conditions, we first set three conditions of fingertip moisture content: standard, wet, and dry. Next, the average thickness and Young's modulus of the stratum corneum were measured by fingertip mechanical characteristics measurement system using an optical coherence tomography (OCT). The stratum corneum thickness of the fingertip is detected from tomographic images. Young's modulus of the stratum corneum of the fingertip was calculated from the pressing force measured by load cell, stratum corneum thickness detected from the tomographic image, and the contact area between the finger and glass plate. Finally, vibration amplitude detection thresholds were measured under each moisture condition using a vibration presentation device. Six different vibration frequencies were used for the vibration amplitude detection threshold measurement. As a result, it was clarified that the thickness of the stratum corneum increased and Young's modulus decreased when the moisture content of the fingertip decreased. It was also confirmed that the threshold for detecting high-frequency vibration was lowered as the moisture content of the fingertips changed.

Tactile illusion is a phenomenon that a stimulus is perceived different from the original physical phenomenon. Various tactile illusions have been confirmed to occur under specific stimulus conditions. Soft-feel grain is the surface that induce illusion which an object's surface changes hardness. In this study, we investigated the effect of surface roughness on the perception of hardness and its factors. In the experiment, tactile samples with the same hardness and different surface properties were used for sensory evaluation of hardness during stroking. During sensory evaluation, the contact state and fingertip characteristics were measured. And we discussed the relationship between the change in hardness. As a result, it was considered that the frictional force between the fingertip and the sample decreased the fingertip speed and subjects felt the sample was non-slip. This feeling of non-slip may cause the sample to feel harder.

Although floor reaction force data is useful for gait analysis, it can only be measured in specialized facilities because it is often measured using installed force plates. This report examines a simple and highly accurate three-directional floor reaction force estimation method based on images taken with devices that most people have. By using only captured images for estimation, we believe that floor reaction force estimation can be easily performed without the need for specialized knowledge, sensors devices, skeletal information including uncertainties obtained from images, and statistics for each body segment. CNN, a type of deep learning, is used for this learning. Generalization performance for untrained subjects is evaluated by cross-validation using data from five subjects. The estimation results were accurate with errors of 8% of body mass in the vertical direction, 2% of that in the medial-lateral direction, and 3% of that in the anteriorposterior direction for a normal gait. Accordingly, the generalization performance of the proposed method was confirmed.

The purpose of this study is to estimate floor reaction forces from measured body part accelerations. A three-dimensional motion analysis system is used for the measurement. In the proposed method, equivalent acceleration is used to derive the floor reaction force. The equivalent acceleration is derived from the equilibrium relationship between the inertial force of the whole body and the floor reaction force. In other words, the equivalent acceleration is the floor reaction force that is made dimensionless by dividing the floor reaction force during walking by the whole body mass. To estimate the equivalent acceleration, a motion mode function that represents the relationship between the acceleration of each measured body part and the equivalent acceleration is created in advance by frequency analysis. Once the equivalent acceleration is estimated, the floor reaction force can be derived by a simple force balance calculation. Therefore, it is possible to estimate the floor reaction force using only the acceleration of one body part. Results of walking experiments, the equivalent acceleration was estimated from the acceleration of the head, and the floor reaction force could be derived with high accuracy.

This study aimed to evaluate the acute effects of post-exercise exposure to an alternating current (AC) magnetic field (50 Hz, Bmax 180 mT, 15 min) on muscle fatigue using surface electromyography (EMG). Ten healthy right-handed male volunteers (mean age 23.7 ± 2.0 years old) participated in the test. Electrodes were attached to the brachioradialis, flexor carpi ulnaris, and flexor carpi radialis muscles of the left forearms of the volunteers to monitor their muscle fatigue after the handgrip exercise/training. The handgrip strength and the intermediate frequencies of the EMG power spectrum were compared between the AC-magnetic-field- and sham-exposed groups. No significant difference between the groups was observed in terms of the handgrip strength, but a significant difference was observed between them in terms of the intermediate frequency in the flexor carpi radialis muscle, suggesting that the exposure of the AC magnetic field could have partially and instantly accelerated the recovery of muscle fatigue.

In recent years, compression garments have been used in sports to improve athletic performance, such as reducing fatigue and extending exercise time. There is no certain view on the effect of compression garments on exercise performance, and the mechanism has not been elucidated yet. Therefore, to elucidate the mechanism of the effect of compression garments on the improvement of athletic performance, in this study, we focused on the relationship between soft tissue vibration and muscle activity. Specifically, the study was aimed at clarifying the effects of compression garments on body surface vibration and muscle activity characteristics during walking, in which impact is applied to the heel. Frequency analysis of the vibrations measured on the lower leg from heel ground contact to heel release was performed. As a result, it was confirmed that the power spectrogram density (PSD) value of the medial head of the gastrocnemius muscle in the circumferential direction of the lower leg became lower when the subject wore compression socks. It was suggested that wearing compression socks greatly suppressed the vibration of the lower leg during exercise.

Japan is a super-aging society and the number of people requiring nursing care is increasing with each day. Maintaining the ability to walk by preventing falls and maintaining and improving muscle strength is key to preventing the need for nursing care. However, most of the conventional gait training is monotonous and it is difficult to maintain motivation. Therefore, a system was developed in this study that enables users to enjoy walking and also maintain their motivation. Using CycleGAN, a machine learning model capable of transforming one image to another, a system was developed that enables walking while transforming real scenery in real-time and presenting it on a head-mounted display, and verifies the psychological impact of the proposed system on pedestrians. A 10 m walking experiment was conducted on males in their 20s, and the results obtained were compared using the two-dimensional mood scale-short term (TDMS-ST) method and a subjective evaluation questionnaire using the visual analog scale as a walking evaluation questionnaire. The results of the experiment showed that the arousal level of the TDMS-ST increased and the values of the items "Did you find walking enjoyable?" and "Did you want to continue walking?" in the walking evaluation questionnaire increased. This suggests that the proposed system can assist with the motivation for walking. However, it has also been suggested that it might increase the feeling of fatigue from walking.

Sharing information among prosthetic hand users and rehabilitation personnel is essential to improve the effectiveness, efficiency, and satisfaction of rehabilitation services that meet the user’s needs. The goal of this research is to establish an online platform for sharing video of pediatric prosthetic limb tasks and skills. The project's objective is to confirm a suitable video filming and processing factor and condition for automated task labeling of the video files. An orthogonal array experiment was conducted using four factors that affect hand detection. Comparison of the estimated and confirmed experimental gains showed that the Signal-to-Noise Ratio was better than the estimated value’s ± 30 %, hence, reproducibility was not confirmed with the control factor setting. Sensitivity was below ±30 % of the estimated value, and reproducibility was confirmed. Although the best condition in this experiment was approximate to the target output, further selection of control factors is required to suppress the variation.

We have been studying two main methods for preventing patient falls and reducing the workload of medical staff at medical and nursing care facilities, using artificial intelligence and robotics technologies. One is a realtime fall risk assessment of patients and their surrounding environment using deep learning. The other is a method to present recommendations and nursing assist to medical staff for optimal interventions for patients using deep reinforcement learning to reduce the risk. In this paper, we analyze the results of incorporating nursing theories into deep reinforcement learning, and introduce the effectiveness, limitations, and future prospects of the application. First, as applications problem of deep reinforcement learning, we apply representative nursing theories of Roy, Johnson, Orem, Henderson, Peplau, Orlando, Abdellah, King, Wiedenbach, Travelbee, Leininger, Newman, to achieve consistency with the medical field. Next,as an effect of their application, we show that it is possible to clarify what information from the clinical field should be used for the main design parameters of deep reinforcement learning, i.e., state, action, and reward. As a limitation of the application, the conventional training and evaluation by reproducing scenes in dynamic 3D simulations can be used to evaluate operational efficiency strategies and safety based on environmental sensing data and external feedback from patients on intervention. However, it is necessary to incorporate internal feedback into the evaluation of the validity of the actions of nursing assist robots and medical staff. Finally, the use of a virtual environment, such as a metaverse with avatars, will suggest future work to solve this problem