As Japan faces a super-aging society, the increasing number of elderly people who are bedridden due to fall fractures has become a major social issue. Hip protectors have, thus, been proposed to prevent femoral fractures in cases of tumbling or falling; however, they are not widely used because the tightness of the equipment and the hassle of wearing it. In recent years, flooring materials with high buffer performance have been attracting special attention in the prevention of bone fractures in cases of tumbling or falling. So far, however, the “floor hardness test,” which is an evaluation method for cephalopathy (concussion of the brain), is the only risk assessment method for injury risks caused by flooring materials, and no such evaluation method is available for femoral fracture risks. Therefore, we fabricated a test instrument (pendulum tester) that reproduces the load that the femur received at the point of falling on the floor and developed a mechanism to assess fracture risks with high accuracy on the basis of the measured load. The pendulum tester is characterized by the following features: (1) has an impactor simulating the shape of the femoral region (made using the femoral computed tomography image of the elderly as a reference) and (2) has a dummy skin reproducing the buffering performance of human soft tissue. On conducting fracture risk assessment of four types of commercially marketed flooring materials using the pendulum tester, we found that the merits and demerits of the safety vary greatly by comparing with the evaluation results of the floor hardness test. The above-mentioned results show that an appropriate flooring material evaluation method should be chosen depending on the lesion site and type of injury.

In this study, by applying the double inclusion method to thermal and electromagnetic problems, micromechanical modeling and analysis is performed for a composite material containing many double inhomogeneous inclusions. In modeling, the inner and outer shapes of double inhomogeneous inclusions are ellipsoid that are different from each other. The interaction field due to the presence of many double inhomogeneous inclusions is evaluated using the Mori-Tanaka theorem. The macroscopic dielectric constants of the composite material are derived explicitly by terms of the difference in shape between inner region and outer one of a double inhomogeneous inclusion. It is shown that the independent number of macroscopic dielectric constants of the composite material is the same as that of an orthorhombic material. For the special case where the shape of inner region and outer one of a double inhomogeneous inclusion are sphere or fiber, the present results are compared with results of the Hashin and Shtrikman's bounds, the Benveniste and Miloh's solution, the Hatta and Taya's solution and the solution derived by the self-consistent method. Furthermore, calculations were performed for the case where the shape of double inhomogeneous inclusions is confocal spheroid. Based on results of these calculations, the validity of this analytical solution is examined.

In this study, quasi-isotropic (QI) laminates were fabricated using two types of PA6/CF thin-ply prepregs with different fiber/matrix interfacial properties, and Charpy impact tests and falling weight impact tests were conducted. The effects of layer thickness of prepreg and interfacial properties on the impact energy absorption performance were investigated by clarifying the fracture mode and propagation during impact. The layer thickness of each ply was set to 40, 80 and 120 μm by using thin-ply prepreg with the thickness of about 40 μm made by tow-spreading technology. Charpy impact values were higher for PA6/CFsmooth, where interface fracture was dominant, the values significantly increased as the layer thickness of the prepreg increased. On the other hand, the Charpy impact values of PA6/CFrough, where cohesive fracture is dominant, did not change significantly with increasing prepreg layer thickness. The results of the drop-weight impact test indicate that the layer thickness of the prepregs changing the fracture mode depends on the fiber/matrix interfacial properties. It is clear that the layer thickness at which the "thin-ply effect = reduced delamination" induced by changes in the layer thickness constituting the QI material is affected by the fiber/matrix interfacial properties. From the viewpoint of impact energy absorption, similar to the results of the Charpy impact test, it was shown that more impact energy can be absorbed when large scale delamination occurred.

Here we propose a new method to generate Kirigami honeycomb for complicated structures. Although commercially available honeycombs have the same cross-section as standard, Nojima and Saito firstly showed honeycombs could be curved by using the Kirigami operation. By this, the Kirigami honeycomb has become a mighty treasure trove of metamaterial creation, so Kirigami has been an international language like Origami and it has been a hot topic in the Origami engineering community. So far, there is an overlap in the development view of the honeycomb core with a non-convex curved surface and the development view cannot be used for the construction of the core with a non-convex curved surface. Moreover, with conventional methods, STL(Stereolithography) data which are often used by the additive 3D printer can be used only after the formulas on the upper and lower surfaces are obtained. Since with the conventional methods, only the structure that can be completed by the information of the upper and lower surface formulas can be handled, they cannot treat a structure with a non-uniform shape between the upper and lower surfaces, and also curvature and thickness can only change in one axis. With this proposed method, firstly the target structure expressed in CAD and/or STL data is covered with a honeycomb core of any shape in any direction. Secondly, the intersections of the two are obtained and at last it is obtained the honeycomb core peculiar to the structure of the prepared honeycomb base. That is, the proposed one is extremely general like the present additive 3D printer. The biggest drawback of the Kirigami honeycomb is that the material yield is not always good for which this proposed method is also advantageous because it can select the orientation of the honeycomb cell in which material yield is maximized.

Molecular dynamics simulations are implemented on the interaction between mode I crack in Fe single crystal and cylindrical Ni/Co/Zr/Mo obstacles, substituting Fe atoms with those elements in a periodic slab cell. The crack penetrates the Ni and Co obstacles while it bypasses the Mo one by the slip and void nucleation at the Fe-Mo interface. The crack also cuts in the Zr obstacle; however, it is caught by the amorphized Zr atoms in Fe matrix, showing remarkable resistance against crack propagation. Then these behaviors are discussed with the eigenvalue/vector of the atomic elastic stiffness coefficient, B^α_ij=Δσ_i^α/Δε_j, where σ_i^α and ε_j are the atomic stress and strain in the Voigt notation. Atoms in the Ni, Co, and Zr obstacles show lower eigenvalue, η^α(1), the solution of B^α_ijΔε_j=η^αΔε_i, against Fe matrix while those in the Mo obstacle have higher one than Fe. That is, the crack cuts in the “soft” Ni, Co and Zr obstacles and bypasses the “hard” Mo one. The unstable modes of crack tip, slip in the obstacles and at the Fe-Mo interface are visualized from the maximum shear direction of the eigenvector of {Δε₁,Δε₂,･･･,Δγ₆}^T={Δε_xx,Δε_yy,･･･,Δγ_xy}^T for unstable η^α(1)< 0 atoms.

A study on separation control mechanisms of tandemly arranged wing with linear leading edge (LLE) and leading edge protuberance (LEP) in low Reynolds number was conducted. In this study, to investigate the separation control mechanism, we carried out the visualization experiment using smoke-wire method, the streamwise and spanwise velocity measurements above the upper surface of the backward wing by using hotwire anemometer, and the numerical simulation. From the results of flow visualization experiment, it was found that the high lift coefficient obtained by tandemly arranged wing with LLE and singly and tandemly arranged wing with LEP were caused by reducing the flow separation region. From the results of velocity measurements and numerical simulation, it was found that in the case of wing with LLE, the turbulence generated by forward wing, which had mainly streamwise component with peak frequency of 230Hz and broadband frequency over than 30Hz, controled the flow separation. Whereas in the case of wing with LEP, regardless of the wing arrangement, separation control was brought by the separation bubble that caused by the longitudinal vortices generated by the LEP. It was also found that the turbulence from forward wing affected the position of the valley part where the separation bubble and the strong negative pressure were formed.

The sound generated by a vortex pair moving close to a rectangular cylinder is studied by high-resolution simulations of the two-dimensional unsteady compressible Navier-Stokes equations at Mach numbers ranging from 0.05 to 0.3. In this study, the Mach number Ma is defined by Ma=V_t /c₀, where V_t is the translation velocity of the co-moving vortex pair and c₀ denotes the speed of sound. The directly computed far-field sound is compared to the prediction of the acoustic analogy proposed by Lighthill (1952) and Curle (1955). The prediction is in excellent agreement with the simulation, where the two-dimensional form of Curle’s modified solution is adopted for an accurate calculation of the sound waves with a phase difference between various vortices around the cylinder. It could be confirmed that the scaling law in two dimensions holds in this simulation. In this study, the sound generation due to the dipole and quadrupole fields is investigated by calculating the two terms in Curle’s analogy. Examining the surface distribution of dipoles on the cylinder indicates that the force exerted on the fluid by the solid boundaries of the side/upper wall of the rectangular cylinder generates the sound when the co-translating vortices approach /pass the rectangular cylinder, which is the sound due to dipoles corresponding to the directivity of the sound in the polar diagrams. The area distribution of quadrupoles which is the second time derivative of the area integral of Lighthill’s stress tensor indicates that the sound is emitted from a vortex generated at the corner of the rectangular cylinder when the vortex pair approaches the cylinder and where the interaction between many vortices around the cylinder and the co-translating vortices generates the sound when the co-translating vortices pass the cylinder.

The purpose of this study was to elucidate collisions between droplets and a liquid film, where the liquid film and the droplets are composed of different liquids. Understanding this phenomenon is important to improve the environmental performance of internal combustion engines. The collision behavior of different liquids under the simplified experimental system is discussed on the basis of experimental results. The impingement of a single droplet on a liquid film was observed using a high-speed video camera. Another observation was carried out to distinguish whether the secondary droplets by splash were derived from fuel or liquid film. The different splash phenomena from the same liquid collision experiment were observed. The collision behavior of different liquids was classified into four categories. The characteristics of the collision behavior and underlying mechanisms were discussed and elucidated. An empirical formula that represents the phenomena was derived.

Tandem control is the control to drive one load with multiple motors. We compare three tandem control methods to suppress the natural vibration of the system: 1) a common torque method, 2) an average rate feedback method, 3) an individual rate feedback method. The common torque method is to feedback the position signal and rate signal from the motor 1 to obtain the torque reference of the motor 1, and give the torque reference to the motor 2 with the correction calculation to equalize the torque. We found that the difference in reduction ratio affects the suppression effect of the natural vibration. The average rate feedback method feedbacks the average position, the average angular velocity, and the rate difference of the motors to execute the tandem control. In addition, it is a method to equalize the torque by calculating a torque correction signal of the same value with a different sign, from the average rate and average current of the motors. The rate difference signal feedbacks through a high-pass filter that passes the natural vibration of the system, so the natural vibration is suppressed in the transient state. The individual rate feedback method feedbacks the angular velocity individually. In addition, it is a method to equalize the torque by calculating its torque correction signal from the rate of the each motor. We could equalize the torque and suppress the natural vibration through this simulation and experiment, in all three methods. We result the individual feedback method is the best, because the common torque method is not able to tune the natural vibration with the control gain, and the average rate feedback method is complicated to tune the control gain.

Human-robot cooperation systems can combine the skills of humans and the power of robots, which can improve productivity and flexibility and reduce the physical burden on workers. Admittance control has often been applied to the collaborative task with physical human-robot interactions. However, in the conventional methods, the admittance parameter was adjusted based on heuristic methods. The authors have proposed an iterative learning control scheme that can update admittance parameters to reduce the physical burden on the operator in the collaborative task. However, there was a problem that the learning performance was significantly influenced by uncertain data such as noise and outliers because the steepest descent method, which has a fixed learning rate, is employed in the updating law. Furthermore, the manual learning-rate adjustment by trial and error was required to improve learning performance. In recent years, research on adaptive gradient methods that vary the learning rate has been actively conducted in the fields of machine learning, aiming at improving learning performance. In this paper, we propose a novel iterative learning control scheme with adaptive gradient methods for human-robot collaborative manipulation to improve the learning performance against uncertain data and lower the cost of adjusting the learning rate. The validity of the proposed method is demonstrated throughextensiveexperiments, including 1) cooperative operations in the presence of obstacles and 2) cooperative transport of heavy objects.

In previous paper the authors successfully developed a vibration suppression device (VSD) that has variable moment of inertia using Magneto-Rheological (MR) fluid. The MR fluid is filled into a flywheel. Ferrite particles of the MR fluid are clustered when magnetic field is applied to the flywheel by electromagnets, series inertia mass of the VSD will be switchable. In this paper seismic tests during switching series inertia mass by reinforcement learning are focused in order to get more vibration reduction while random excitations. Firstly, agents are trained by the reinforcement learning using Deep Deterministic Policy Gradient (DDPG) algorithm while a one-degree-of-freedom system with the VSD, which has the switchable series inertia mass, is excited under earthquakes. Secondly, the VSD is improved for having 8 electromagnets, magnetic field is analyzed by FEM, resisting force characteristics and response performance of the VSD are investigated. Then, to confirm the vibration control under some earthquakes, seismic tests of one degree-of-freedom system with the VSD under the reinforcement learning using DDPG are carried out by a shaking table, and seismic responses are simulated numerically. From the experimental results, the peaks of response acceleration and displacement decrease about 1/2 in case with the VSD using DDPG, and also cut 20 % by switching series inertia mass. Finally, validity of vibration reduction during switching series inertia mass by the reinforcement learning is confirmed.

The pressure for supporting the bearing load is induced by the generation of discontinuity of the shear flow rate in each region only by arranging areas in the slip direction with different slipperiness of fluid. In this report, the generated pressure and friction characteristics, which were important for clarifying the characteristics of disc type partial slip thrust bearing were investigated using three-dimensional modified Reynolds equation considering the slip on the solid surface. It was suggested that the relationship between the shear rate and the slip length which is determined with the film thickness estimated from the friction force measured in this bearing by assuming a pure shear condition can be treated as a two-term slip model. Finite width analysis was performed assuming critical shear rate and constant slip length, and the Stribeck curve and pressure distribution were obtained. The low shear rate region less than critical shear rate is increased in the center side of the disk type bearing for the lighter load and the thicker film cases. Then, the friction for supporting the same load shows the value higher than the friction where slip occurs on the entire surface of the assumed slip area of the bearing. On the other hand, since the entire slip area of the bearing surface approaches a slip state, the film thickness and friction when supporting the same load are the same as those when the entire assumed slip area is on slipping. The influence of such critical shear rate also appears in the results of the radial pressure distribution in disc type bearing, and the calculated pressure on the inner circumference side rapidly decreases due to the presence of the non-slip region on the inner circumference side with low shear rate. And then, this tendency agrees with that of the measured radial pressure distribution.

Plastic injection molding (PIM) is a manufacturing technology to plastic products, and it is important to determine optimal process parameters for high product quality and high productivity. Weldline that are formed when two or more melt fronts meet should be reduced for high strength and high surface quality. Rapid heating cycle molding (RHCM) that the mold is heated up is an attracted PIM technology for weldline reduction, but long cycle time is generally required. In this paper, an RHCM incorporating a heater system is used, and the process parameters optimization is performed. To determine the optimal process parameters, multi-objective optimization for minimizing both weldline and cycle time is considered. The numerical simulation in RHCM is computationally so expensive that sequential approximate optimization that the response surface is repeatedly constructed and optimized is adopted for the design optimization. The pareto-frontier is identified through the numerical simulation, and the experiment using PIM machine (MS100, Sodick) is also conducted. It is found from the numerical and experimental result that the RHCM using the heater system is effective to the weldline reduction.

Tactile graphics containing only dots have long been widely used. However, tactile graphics containing only dots may be mistaken for braille. This study aimed to investigate the influence of distance between dot pattern and braille in tactile graphics by emboss printing method on the ease of braille identification. Test pieces with varied distance between dot pattern and braille in tactile graphics were created using EDEL software, which is a de facto standard in Japan, and printed using the ESA721 braille printer (JTR Co.). Sighted subjects who were beginner braille readers and subjects with visual impairment who were expert braille readers were asked to identify the test pieces. The results showed that the visually impaired who regularly use tactile charts and braille could identify braille accurately, quickly, and with confidence when the vertical and horizontal distance were 4.7 mm or greater. For novice braille readers, they were able to identify braille accurately, quickly, and confidently when the vertical distance was 5.9 mm or greater and the horizontal distance was 4.7 mm or greater. These results indicate that the novice readers can identify braille correctly, quickly, and confidently when the vertical distance is 5.9 mm or greater and the horizontal distance is 4.7 mm or greater. In addition, test pieces with extended vertical distances were easier to identify than those with extended horizontal distances.

A noncontact estimation method of three-dimensional position of simulated blood vessel in an artificial skin model and an automatic puncture method are proposed. Unlike the conventional 3D position measurement method which requires detection of specific points from captured images, the simulated blood vessel filled with simulated blood is captured using two infrared cameras and the vessel image taken is approximated by a linear equation. The two equations of the plane containing the linear equation and the focus of each camera are obtained. The intersection of two planes is the center axis of the simulated blood vessel and is defined by a 3D linear equation. A six degree-of-freedom robot is developed to perform automatic puncture. The position of puncture needle is controlled by cartesian coordinate mechanism to achieve high reliability and precision when operating in three-dimensional space. The direction of needle is controlled by rotational mechanism using two stepper motors with small backlash. Straight movement of puncture needle toward the simulated blood vessel is achieved by a linear actuator activated using a DC servo motor. A three-dimensional force sensor attached at the needle and a photo interrupter placed across the blood collecting tube are employed to monitor puncture procedure. Sudden decrease in puncture force indicates the penetration of upper wall of simulated blood vessel. Light blocking in photo interrupter shows blood flow into tube. Twenty kinds of automatic puncture experiments are performed on simulated blood vessel of 2 mm or 3 mm in diameter and 4 mm or 6 mm in depth, changing direction every 10 deg from 20 deg to -20 deg in phantom which simulates mechanical characteristics of human skin. Experimental results show that 17 experiments were successfully punctured, and the effectiveness of the position estimation method of simulated blood vessel and control method of puncture robot system are confirmed.

Perturbations in sitting posture, represented by the center of mass (COM) of the upper body, provide critical information for analyzing balance control. While the COM is generally measured by an optical motion capture system, it is not practical. In a previous study, we proposed a method to estimate the COM during standing from a force platform under the feet based on inverted pendulum models. However, it is unclear whether the technique can be applied to the sitting posture. Furthermore, it is also unclear whether two force platforms under the buttocks and the feet would be required if it could be applied. The purpose of this study is to estimate the upper body COM of a subject sitting on a backless seat from one or two force platforms and to validate the estimation accuracy by comparing the results to those from an optical motion capture system. For considering forces acting from the lower limbs, it is necessary to adopt a mechanical model that includes the lower limbs and to use a force platform under the feet in addition to those on the seat. We compared estimation accuracy between the models with and without lower limbs in three conditions: rest sitting, voluntary sway, and seat sway with an electric cart. The result indicated a clear difference between the two models, and the model considering lower limbs had high accuracy. Since the present method is a practical and highly accurate method of sitting posture, it may be applied in the analysis of low back pain and motion sickness.

This paper discusses explanatory variables that constitute the driver’s subjective risk level when encountering a pedestrian who suddenly pops out from the roadside. In this research, near-miss incident data, called “Hiyari-hatto data,” against pedestrian recorded by drive recorders equipped on taxis are used. First, we evaluate the subjective risk level of 90 near-miss incidents quantitatively in 6 levels and select the candidate of eight explanatory variables. Second, Principal Component Analysis (PCA) is applied to determine the principal components of the subjective risk level. Moreover, Multiple Regression Analysis (MRA) is used to compare the contribution of explanatory variables. From these analyses, some explanatory variables have become effective candidates. Time to collision (TTC) and its related variables might be the main explanatory variable and collision timing might be another explanatory variable. However, it is difficult to determine that collision timing is a sufficiently influential variable by PCA and MRA. Therefore, the latter of this paper examines the possibilities of collision timing (in our experiment, qualitative collision timing was evaluated using quantitative value as “collision gap” which is the difference between TTC and TTV) as a candidate explanatory variable by an actual vehicle test. To reveal the relation between subjective risk level and explanatory variables, in particular the collision gap, the driver’s several reactions are collected by an actual vehicle test in which a pedestrian suddenly pops out from the roadside to in front of the vehicle. Based on the about 900 case experimental data, we examined the possibilities of “collision gap” as an explanatory variable in subjective near-miss incident level.

Toward an advanced high-speed railway system, there are ongoing extensive studies on both of railway vehicles and infrastructures. Reducing the aerodynamic noise emitted from the pantograph heads is one of the most important subjects for high-speed railways from the environmental point of view. In order to reduce such aerodynamic noise, several shapes of cross-sectional profile have been investigated. A suitable configuration of the pantograph head with a smooth cross-sectional profile has been proposed. Furthermore, not only aerodynamic noise characteristics but also high contact performance is desired in pantographs. To improve the contact performance, it is important to reduce the mass of the parts that touch the contact wire. Consequently, the contact strips are often supported by springs. However, the pantograph head with a smooth cross-sectional profile and the conventional suspension system of the contact strip sometimes cause undesirable lift force characteristics as a result of the variations in the cross-sectional shape due to the operation of the suspension system. For this reason, authors have developed the multi-segmented pantograph head, which employ novel suspension systems that prevent the abnormality of the lift force characteristic. This paper describes the configuration and mechanism of a multi-segmented pantograph head with offset support, the dynamic characteristics and the validation results of the suspension system by bench test equipment in detail, comparing with the test result of the conventional pantograph head. Finally, the contact performance of a multi-segmented pantograph head is validated in current collection testing equipment with actual catenary system. The test results show that the multi-segmented pantograph head has high contact performance up to high-speed region.

To clarify the behavior of railway vehicles under crosswind, a new method using the left-right balance of air spring pressure is presented in this paper. The rate of off-loading, which is an evaluation index for vehicle behavior, can always be estimated by the new method without conventional special wheel-set. The method is theoretically derived and the accuracy is experimentally verified comparing the new method with the conventional method. In the experiment, lateral forces equivalent to crosswind were loaded statically or dynamically, and a running test was conducted. The results show that the new method and the conventional method are in good agreement and that the new method is useful when analyzing vehicle behavior under crosswind. By applying the practical method to the Shinkansen, it is possible to obtain statistical data on vehicles running at higher speeds or under higher wind speeds easily than with conventional methods. Much data was analyzed on the relationship between wind speed and the rate of off-loading, and the validity of the Kunieda’s equation used for vehicle design under crosswind is verified. This method can monitor effects of crosswind on vehicles not only at specific points but also along railway lines. Therefore, it is possible to identify areas where vehicles are likely to be affected by strong winds. Some examples further improve safety against strong winds are shown in this paper.