It is expected that the vibration characteristics of NC machine tools are affected by the contact between tool and workpiece during the cutting operations. However, the influences of the contact have not been clarified up to now. This study investigates the influence of contact between tool and workpiece onto vibration characteristics of machine tools. In this study, frequency response of a vertical type milling machine during cutting operation is evaluated. The evaluation tests of the contacting effect are carried out with and without cutting operations. In order to clearly evaluate the influence of the contact between a tool edge and a workpiece, boring operations of 50 mm diameter are carried out. The frequency responses are measured by using feed motor torque. Impulse signal is applied to the motor torque command during the cutting operations to oscillate the machine tool, and the axial acceleration of the table is measured to obtain the frequency responses. The impulse signal can be applied by refereeing the spindle rotational angle to control the relationships between the cutting edge and workpiece surface. As the results of the evaluations, it is clarified that the proposed method can evaluate the influence of the contact adequately. The natural frequency slightly increases and the vibration amplitude decreases when the tool contacts with the workpiece, regardless of whether non cutting or cutting. It has also been confirmed that the vibration amplitude of the frequency characteristics is changed due to the contact length of the cutting edge.
Electrochemical discharge machining (ECDM) is a machining method for inorganic insulators. When a tool electrode is fed at a constant rate, the removal rate is often decreased due to enlarging the gap length between the tool electrode and workpiece. In this paper, the effects of the applied voltage, which is a changeable condition during ECDM, and the initial gap length between the tool electrode and workpiece on the current waveforms and machining performance were experimentally investigated. Soda lime glass was machined with a tungsten electrode in NaCl solution. Plenty amount of bubbles were generated below an applied voltage of 45 V, and the removal amount was large. Though discharge strongly occurred over 50 V, the removal amount was small. With an increase of the applied voltage, lower frequency components of the current measured during ECDM were decreased. The initial gap did not affect the current waveforms. The mixture of long and short pulses accelerated removal at a low applied voltage. The phenomena around the tool electrode such as the bubble generation and discharge were distinguished by the principal component analysis (PCA). After a series of current pulses was divided into 12 periods, their statistical parameters were calculated, and the frequency components were calculated by the first Fourier transform. In both the cases, the applied voltage was distinguished by the PCA. The principal components obtained from the statistical parameter performed as essential parameters.
In current mechanical machining technology, it is not easy to form an internal space shape inside a metal workpiece through a small-diameter entrance hole only by removal process. On the other hand, EDM is one of thermal machining methods that removes the material by the high temperature of discharges, and the tool electrode does not contact to the workpiece. The machining force acting on the electrode is very small. Therefore, it is highly expected that internal space shape may be machined if an optimum electrode structure can be designed. This study proposes a new internal space machining method by EDM using a revolution ball electrode consisting of a vertical rotation rod, a tilting rod, and an electrode ball. Experimental results show that the tilting angle between the vertical rotation rod and the tilting one can be changed by the rotation speed, and the electrode ball position can be controlled. Then, machining of some axially-symmetric spacial shapes, such as cylindrical shape and spherical one into a zinc alloy workpiece was succeeded. In addition, machining of internal space shapes by simultaneous two-axis control of the tilting angle and Z coordinate of electrode was possible. Therefore, this method has high possibility to create axially symmetric spatial shapes inside the metal.
The generation of burrs is unavoidable in most cases of mechanical machining. Leaving the burrs on the workpieces may cause various problems, thus the deburring process is necessary. Deburring process requires exclusive tools, and the tools are difficult to apply the workpieces with complicated shape. Laser machining is noncontact process thus it does not cause the deformation of workpiece and tool wear. Especially, fiber laser beam can be transmitted by flexible optical fibers so that it is easy to handle. The purpose of this study is to clarify the processing condition for achieving desired chamfering width with fiber laser. A series of experiments were performed by providing fiber laser beam to ferrous block’s right angle edge. In the experiments, the assist gas direction, the laser power, the processing speed, and the beam diameter were defined as processing parameters. Experimental results confirmed that defocused fiber laser beam can apply to chamfering ferrous materials. It also became clear that processing time can be shorten by processing fiber laser chamfering with higher laser power and higher scan speed. In addition, the results confirmed that the chamfering width is controlled by altering processing parameters as the input energy per unit time and unit volume are kept constant. Furthermore, the burrs on right angle edge can be removed by fiber laser, and the shape of deburred edge becomes rounded.
To realize carbon fiber reinforced plastic (CFRP) mirrors, the high-precision polishing of an epoxy resin surface, which is the reflection surface of such mirrors, is required. To polish the surface with high quality, it is necessary to know the polishing characteristics of epoxy resin. However, unlike acrylic resin, there are few studies in which the polishing characteristics of epoxy resin were investigated. In this study, we polished test pieces of epoxy and acrylic resins in the same single batch under various conditions, and compared their removal rates. For this purpose, a new polishing technique that enables the simultaneous polishing of different materials under the same conditions was developed. We also evaluated the surface roughnesses for both resins before and after polishing. As a result, we found that the removal rate of epoxy resin was approximately 90% lower than that of acrylic resin under the polishing conditions using alumina abrasive grains and a suede pad. The roughness of the resulting epoxy surface was 4.76 nm RMS, which satisfies one specification of optics used in a space telescope.
It is difficult to machine permanent magnets by traditional machining because of brittle-material and magnetic force, but EDM can machine permanent magnets easily. However, because magnets have a Curie point, the reduction in the magnetic flux density may occur in EDM where the machined surface becomes high temperature. In previous studies, when 1 mm removal machining was performed for the cylindrical neodymium magnet, the magnetic flux density decreased in the region of several millimeters directly below the machined surface. When the magnet internal temperature was measured individually for several depths, the region where the magnetic flux density decreased was up to about the upper temperature limit. In this study, to improve the accuracy of temperature measurement, three points were measured simultaneously. In addition EDM was performed for the magnet with different initial magnetizing ratio before machining, and it was made efforts in EDM characteristic of the machining. As a result, in spite of the same discharge conditions, it was found that the magnet internal temperature during machining varies greatly due to the difference in initial magnetizing ratio. From the classification of the discharge state, it was found that these differences were affected by the reattachment of the debris to the magnet.
Demand for high precision machining of complicated shapes has recently increased with the miniaturization of mechanical and electronic products. Therefore, further development of fine wire electrical discharge machining (EDM) technology using a thin wire electrode has been also requested. However, there might be a limit in improving the machining performance of fine wire EDM using conventional wire only by optimizing discharge pulse conditions and gap control. Therefore, it is essential to develop a new type of thin wire electrode for further improvement of wire EDM performance. In this study, high-zinc-content brass (γ-phase brass) coated steel core wire as a new type wire electrode was trially made to improve the machining stability. In wire EDM, zinc content of wire surface would contribute to rapidly cool down the gap by the evaporation due to its low boiling point. However, the surface of γ-phase brass coated wire tends to become rough in the heat treatment process of the wire. Thus, another type of the γ-phase brass coated wire with smoothed surface was also made by an extra finish drawing. The wire EDM characteristics using these wires were compared with those using conventional brass coated steel wire. Furthermore, the distribution of spark locations during process was evaluated by high-speed observation to investigate the influence of γ-phase brass and the surface roughness of wire. As a result, the cutting speed using the γ-phase brass coated steel wire with smoothed surface is faster than that using conventional wire because of uniform distribution of spark location.
Ion beam etching is effectively used for the fabrication of high-precision optics. The main application of ion beam etching is to figure large optical surfaces to correct shape errors remaining on polished surfaces. To figure small or medium-size optical surfaces, the generation of an ion beam with a smaller diameter and a higher ion current is required. In this study, we designed a magnetic lens with quadrupole magnets using neodymium magnets to obtain an ion beam with a small diameter. The magnetic lens is installed between the outlet of an ion gun and a chamber, which enables the trajectory of the ion beam in the chamber to be changed. The trajectories of the ion beam and the ion particle distribution on a workpiece surface when a doublet or a triplet magnetic lens was used were simulated. Simulations were also conducted for ion beams with large and small emittances entering a magnetic lens. In the simulations, the ion beam without a magnetic lens was approximately 30 mm in diameter on a workpiece surface. The simulations showed that the doublet magnetic lens can converge the ion beam on a workpiece surface to an area of approximately 6 mm × 10 mm when the emittance is small. However, this lens is less capable of converging the ion beam in one direction when the emittance is large: the ion beam was converged to an area of approximately 6 mm × 27 mm on a workpiece surface for the large emittance. On the other hand, the triplet magnetic lens can converge the ion beam for both large and small emittances: the ion beams with large and small emittances converged to areas of approximately 4 mm × 4 mm and 10 mm × 5 mm, respectively.
For poly-dispersed nanoparticles, which have more than two peaks on their particle size distribution (PSD), it is important to determine the mean particle diameter and their dispersion at each peak in a liquid. Dynamic Light Scattering (DLS), that is one of a typical nanoparticle sizing method, has difficulty to determine the several peaks in the PSD for the poly-dispersed particles. On the other hand, Image analysis methods (IA) can distinguish the peak for both the primary particle and secondary particle in the PSD of poly-dispersed particles accurately. However, IA is a time-consuming method and it is difficult to apply the measurement of the PSD due to the requirement of measuring the large number of particles, one by one. The particles in the liquid are transferred to a substrate in air when observing the particle to measure their size and the size distribution. In this procedure, some particles usually aggregate with surrounding particles. It causes the difference between the PSD for dispersed particles in liquid and that of the particles on the substrate. In this study, we suggest a novel particle sizing method using “Nanoparticle chip”, that is nanoparticles grid on the substrate to maintain the poly-dispersed condition in the liquid, to develop IA for measuring the poly-dispersed particles in liquid. The dispersed condition of the particle on Nanoparticle chip can be kept from the condition in liquid when the particles are transferred to the substrate in air. Therefore, measuring the PSD on Nanoparticle chip is equal to measure the PSD in the liquid. In this paper, in order to verify the feasibility of the nanoparticle sizing using Nanoparticle chip to measure the PSD for poly-dispersed particles in the liquid, we performed a fundamental experiment to fabricate the Nanoparticle chip and to determine the PSD for poly-dispersed particles. In this report, it is reported that the PSD for the poly-dispersed particles, which is the mixture of 152nm particle and 498nm particle, using Nanoparticle chip.
Plating is a quite important technology used in a variety of sectors such as industrial products and decorative accessories. It is a special processing technology that handles various chemical substances and consists of long serial processes, plating is likely to encounter quality problems. Therefore, it is necessary to realize a method to maintain and manage plating process and evaluate the quality of plated products. The purpose of this study is the state recognition in the plating process and the quantitative evaluation of the quality of the processed surface using hyperspectral data for electroless nickel plating. The hyperspectral data is a combination of two-dimensional spatial information and spectral information with high wavelength resolution. Actual process recognition system with a hyperspectral camera was constructed to obtain and analyze the hyperspectral data of both the plating solution and the processed surface based on multivariate analysis. The non-contact and high-speed monitoring method could be realized to estimate phosphorous acid concentration which causes deterioration of plating solution. Furthermore, the quantitative evaluation of plating surface with newly defined parameters was proposed, and the monitoring results confirmed the validity of the proposed method.
One of the seismic design methods for the steel containment vessel (SCV) of nuclear power plant is established by the Japan Electric Association as JEAC 4601-2015: Technical code for aseismic design of nuclear power plants. The buckling evaluation formulas for SCV in JEAC 4601-2015 are based on a number of buckling test results of various cylinders conducted by NASA (National Aeronautics and Space Administration)(1968) and considered a safety margin. The SCV shall be designed simply and conservatively using the formulas. Recently, the buckling evaluation method using static elasto-plastic buckling analysis has been studied and applied to vessel structures, such as the reactor vessel in fast breeder reactor plant. The elasto-plastic buckling analysis can consider seismic load distributions, openings, initial imperfection of vessel and stress-strain relationship directly in the analysis model, and can evaluate the buckling behavior and buckling load more realistically and reasonably compared to the design formulas. However, the buckling loads calculated by the elasto-plastic analysis are strongly affected by the analysis condition such as material properties, mesh size and initial imperfection shape, and it might be overestimated. In this study, the elasto-plastic buckling analyses for the buckling test of steel cylindrical vessel corresponding to the dimensions of SCV were carried out in various analysis conditions to confirm the sensitivity of buckling load and to establish the analysis procedure and the analysis conditions that can calculate the buckling behavior and buckling load of SCV conservatively and rationally. In addition, to verify the effectiveness of the proposed buckling design method by analysis, the elasto-plastic analyses in accordance with it were conducted for a series of buckling tests of steel vessels with or without stiffening rings. As a result of these analyses, the applicability of the proposed buckling design method by analysis was confirmed.
In order to develop novel direct manufacturing of ABS resin on Al alloy surface by the 3D printing technique with high interfacial strength, the influences of the temperature and the roughness of the Al-alloy substrate, and the cooling rate after manufacturing on the bonding strength of an additive manufactured ABS-resin/Al-alloy dissimilar joint were investigated. The experimental results reveal that the mechanical interlock mechanism is a primary factor for the adhesion between ABS resin and the Al alloy. Besides, there was optimum surface roughness to improve the interlock effect of the ABS-resin/Al-alloy joints; the high bonding strength was able to be achieved under the condition of the relatively fine roughness of the substrate surface. The surface temperature of the substrate was also an essential factor in getting high bonding strength. The interfacial strength increased with increasing the surface temperature of the substrate because the ABS-resin was able to easily penetrate the subtle depressions of the substrate surface due to the improved resin fluidity. However, the interfacial strength decreased due to high thermal residual stress in the case of a much higher condition of the surface temperature of the substrate. From the experimental results, the optimum process condition to achieve about 10MPa adhesion strength was presented.
In order to investigate the effect of hydrogen on Slow Strain Rate Tensile (SSRT) test of austenitic stainless steels, SUS304, SUS316 and SUS316L, two types of SSRT tests were conducted. One is the external hydrogen SSRT test that was conducted in hydrogen gas at temperatures of T = −40 ~ 200℃ and pressures of p = 87 ~ 115 MPa using non-charged specimen. Another is the internal hydrogen SSRT test that was conducted in ambient air or 0.1 MPa nitrogen gas at T = −120 ~ 200°C using hydrogen-charged specimen exposed to hydrogen gas at p = 68 or 100 MPa. SSRT properties (i.e., relative reduction in area, RRA, and relative tensile strength, RTS) obtained in the external and internal hydrogen tests corresponded to each other. The results inferred that the internal hydrogen test can be a substitute for the external hydrogen test. Furthermore, the temperature dependence of RRA and RTS was evaluated based on the austenite stability of materials, which was represented by Md30 temperature, in association with martensitic transformation-induced plasticity. It was found that RRA and RTS of SUS304, SUS316 and SUS316L having different austenitic stabilities were successfully unified by using the novel parameter, T−Md30.
Electrolyzed water generator can produce acidic and alkaline water from tap water and electric power, and is expected to have applications in the food and medical fields for sterilization, cleaning and disinfection. However, there are still many unknowns about the internal phenomena of the electrolytic water production system, especially the two-dimensional phenomena that have a strong influence on the miniaturization, power saving, and longevity of the electrolyzed water generator. In this study, multi physics modeling of electrolyzed water generator and two-dimensional numerical simulations are conducted to elucidate the fluid, electrochemical, and electrical phenomena in an electrolyzed water generator. The numerical model is built with governing equations from fluid dynamics, electrochemistry, and electrodynamics. The results show that the neutralization reaction with hydrogen carbonate (HCO3-) is an important reaction in electrolyzed water generator, and this reaction divides the anode cell into two regions (low pH region and high pH region), and the electrical conductivity is low in the low pH region. This region with low pH and electrical conductivity extends to the mainstream direction. The current density on the upstream of anode is higher than that of the downstream of anode. This occurs since the region with low electrical conductivity becomes increasingly thicker moving downstream.
A new type of wave power generation system was proposed by using bending plate type generator installed in a vertical slit type breakwater. The system has some advantage compared with other systems; namely, (i) no occupation of the sea surface, (ii) maintenance facility, and (iii) high energy efficiency by using accelerated flow from the slit of breakwater. The generator has a quite simple structure composed of a rectangular plate or cloth connected to a wheel and axle via a string set in the water chamber. When the wave drag bends the plate or cloth, a tension appears in the string and it rotates the wheel connected to a generator. In this report, the maximum output obtained in 1/12 scale model experiment was examined by changing the size of the bending plate. In addition, we also examined the float type power generation mechanism using the water level change in the water chamber and evaluated the output when combined with the bending plate. The experimental results showed that the output of the proposed system per unit sea area is superior to those of the other types of generators
A test on the water tightness performance of watertight doors was conducted to obtain knowledge on the fragility beyond design conditions. The performance test was conducted on three types of standard single-swinging watertight doors used for nuclear facilities. Assuming tsunami conditions during an earthquake, the water pressure and the shear strain caused by horizontal force were applied on the watertight door during the test. A shear strain of up to 4000 μ and a water pressure of up to 0.3 MPa were loaded step by step. The water that leaked from the door was measured at each step. The test results showed that the water pressure was related to the leakage quantities, but no clear relationship was observed between the shear strain and leakage quantities. Subsequently, a confirmation test was conducted focusing on the sealed portion of the watertight doors. The condition of the packing and the leakage of the seal during water pressure loading was observed. Consequently, we found that a large quantity of leakage under water pressure was caused by protrusion of the packing, and we inferred that leakage would occur by the same mechanism in actual watertight doors. Using the test results, we considered a method for evaluating the water tightness limit of the door. An analysis on the performance test was conducted using the evaluation method. The result showed that the water pressure that formed a leakage path in the analysis was consistent with the water pressure that caused a large quantity of leakage in the test.
In this study, the thermal conductivity of porous insulation materials and vacuum insulation panel (VIP) composed of glass wool were measured under different temperature conditions using a high-precision guarded hot plate (GHP) apparatus developed by author’s research group. This GHP device used a Peltier module to measure the temperature difference between the main plate and the guard plate. The temperature fluctuation of the Peltier module is ± 20 μK, which is 500 times more accurate than the commonly used thermopile. The element of the thermal conductivity of the porous heat insulating material were classified. The expanded uncertainty calculated with the inclusion coefficient kcf = 2 was 0.25% or less for the porous insulation and 0.51% or less for the VIP composed of glass wool. It can be expected that the measurement of thermal conductivity is highly accurate. Moreover, it was confirmed that the measured value of effective thermal conductivity was linearly proportional to the cubic of temperature. It has been experimentally shown that the equivalent radiative thermal conductivity of the porous insulating material and VIP composed of glass wool occupy from 30% to 50% and 36.0% under normal temperature environment 20 °C respectively. Furthermore, the effective thermal conductivity of VIP and its punched one were compared. It was clarified that the thermal conductivity of the porous insulating material was suppressed by about 75% under the vacuum environment. Evaluating the thermal conductivity component of effective thermal conductivity in the porous insulation material, the variation of the solid thermal conductivity by the changing of the porosity was discussed qualitatively.
This study experimentally investigates the effect of the impinging spray flame on the local heat transfer to the impinging wall. The experiments were conducted using the rapid compression machine (RCM) equipped with heat flux sensors installed into impinging wall to measure local instantaneous wall temperature. The injection pressure, the ambient density and the impinging distance between the injector nozzle and the impinging wall were varied independently as experimental parameters. The results show that when the liquid spray impinged on the wall, the local heat transfer at the impinging point was suppressed due to reduction of temperature gradient between the wall and the high temperature burned gas. The relationship between the local Reynolds number and the local Nusselt number was different from the time series plot and the average plot. The exponent n of the local Reynolds number in the empirical equation of the Nusselt number was increased by increasing impinging distance at the impinging point and the offset point. Furthermore, with increasing impinging distance, the value of exponent n of the local Reynolds number at the offset point approached the value of the exponent n at the impinging point.
When a mobile robot moves in an environment where there are moving obstacles such as pedestrians and other robots, the robot is required to avoid collisions with these obstacles. However, trying to avoid all the predicted positions on the trajectory of the moving obstacle would overly restrict the robot’s movement. In order to solve this problem, we should be able to generate trajectories in which the robot and moving obstacles do not approach at the same time in the future. However, an approach such as optimizing the robot’s trajectory for the predicted trajectory of a moving obstacle would result in a very large number of states to be considered. This paper proposes a method to generate a set of candidate trajectories based on the robot’s motion model and determine the trajectories considering the collision probability with the predicted trajectories of moving obstacles at each time. In the proposed method, the action of the robot is determined by the following process. First, candidate trajectories of the robot based on its motion model are generated. Next, at each time step of each candidate trajectory, the collision probability with each obstacle is calculated. The same calculation is made for all obstacles and the collision probability with one or more obstacles is calculated. If the maximum probability of a candidate trajectory is greater than the threshold, the trajectory is considered dangerous and is removed from the candidate list. Depending on the distance from the target, the robot selects a trajectory from among the remaining candidate trajectories and determines the next action. In a simulation environment with 30 moving obstacles, the performance is compared with other methods and shown to be comparable or better. In addition, experiments using a real robot were conducted to show the usefulness of the proposed method.
In recent years, the demand for fine particle materials has been increasing in various industrial fields such as electronics, chemistry, and medicine. Ball mills are commonly used for the production of fine particle materials, but they have some problems. In particular, when the rotation speed is increased, the contents stick to the inner wall of the container and rotate together. That is called the critical condition, and the efficiency is significantly reduced. The three-dimensional ball mill, which rotate its container with two degrees of freedom, is proposed as a solution to overcome such problems. We found that the critical condition is suppressed by using three-dimensional ball mills. It was also reported that both frictional heat generated during pulverization and particle unevenness are reduced. Although some advantages can be found with this machine, there is few theories that explain what has been happened. In this study, we focused on the mechanism of suppressing the critical condition. First, based on the past study for ordinary ball mills, we created a theoretical formula for three-dimensional ball mills in critical condition. Next, using the formula, we simulated the motion of three-dimensional ball mills. Finally, we compared the simulation with the motion of the actual machine, and confirmed that they agreed well.
Movement of knee joints include rolling and sliding. To assist the standing movement, we developed two types of passive assist devices with bio-inspired knee joints (BKJ); movable-shaft passive device with BKJ (MSP-BKJ), and single-shaft passive device with BKJ (SSP-BKJ). The MSP-BKJ composed of a fixed noncircular gear, a circular gear, and torsion springs. The SSP-BKJ, in contrast, composed only of an ellipsoidal cam, and torsion springs. The motion of the rotational shaft of the MSP-BKJ was designed to mimics the motion of human joints, in contrast, the rotational shaft of the SSP-BKJ does not move. In order to compare their performances on the supporting effect and burden on the skins, we evaluated the electromyogram (EMG) of lower limbs and shear stress between users’ skin and two types of the assist devices. Shear-force sensitive sheet (SSS) was used to assess the shear stresses on the skin. Although, the EMGs did not show significant differences, the shear stress in the case with the MSP-BKJ was significantly lower than that with the SSP-BKJ.
In this paper, we propose a novel robotic action/observation planning method for playing“ Yamakuzushi ”game which is a Japanese board game selecting one Shogi piece from the randomly stacked pile and sliding it off the board. In our proposed method, we first select one of the pieces from the pile by referring a human operation characteristics. We use the CNN trained by using the depth image of the pile and the result of human operation. To successfully slide the selected piece off the board without making collision with the neighboring pieces, we formulate the action/observation planning based on the partially observable Markov decision process (POMDP). We select the view pose to obtain enough visibility of the pile around the selected piece. After obtaining the visibility, we determine the direction of piece’s motion to avoid the contact with the neighboring objects. The effectiveness of the proposed method is confirmed by experiments.
Localization in autonomous vehicles is an important technology, and the use of 3D point clouds, which provide accurate information on the road surroundings, has been attracting attention to help improve localization. In recent years, many methods for constructing 3D point clouds have been proposed for use in autonomous vehicles. However, 3D point clouds can be misaligned due to errors in measurement high accurate sensors, and so on, which causes the failure of localization. Therefore, it is important to confirm the accuracy of the 3D point clouds and the feasibility of high-accuracy localization in advance. The accuracy of 3D point clouds is often confirmed via simulations using sensor data collected by vehicles if the localization is sufficiently accurate. However, the applications of 3D point clouds are expanding, and it would be preferable to avoid using sensor data for misalignment detection. Therefore, in this paper, we propose an indicator to detect the location of the misalignment of a 3D point cloud constructed by Mobile Mapping System, using only the 3D point cloud as an indicator of convergence and similarity of the ground objects via matching. The effectiveness of the proposed method was confirmed by the evaluation test, which showed that the proposed method can detect positional shifts in 3D point clouds even at locations containing similarities among geological features.
In recent years, the number of senior citizens needing nursing care has been increasing rapidly. Pressure ulcer is a major health issue for such people. In this study, for early detection of pressure ulcer, we developed a monitoring system by using a fabric sensor sheet that can monitor the degree of progress of pressure ulcer daily. This sheet is made using conductive knitting, and it functions as a sensor for measuring body pressure distributions of a user sleeping directly on the sensor sheet. It does not disturb the movement of the user and has an advantage of superior breathability and flexibility in comparison with existing pressure sensors. Moreover, our new design comprises a laminar structure for the wiring of the device, for ease of use. We measured the sleep postures of six subjects using this system and monitored those clearly. For our experiment results, we used a deep neural network (DNN) to distinguish each sleep posture and used a support vector machine (SVM) to determine the positions that caused pressure ulcer the most. As a result of these examinations, we showed that it was possible to distinguish the sleep postures with a high accuracy of 98% or more, and it was also possible to identify the positions that caused pressure ulcer the most.
In this study, we propose a device for isotonic training of tongue-pushing movements. This device realizes dynamic constant external force resistance training by applying a constant load by a DC geared motor to the tongue during the tongue up-and-down movement. This has a back-drive capability by using a series elastic actuator (SEA) with elasticity in the transmission shaft, and the force can be controlled without using a torque sensor. In addition, vibration is damped by impedance control to ensure a safe response for the tongue movement. The tongue muscle ability of five healthy subjects was evaluated using the proposed device. Subjects with higher maximal isometric contraction rates also had higher rates of upward and downward movement at light loads (1.5 N), but subjects who were able to quickly vocalize /ta/ syllables at oral diadochokinesis (OD) rates tended to have less tongue movement when using this device. From the experimental results, it was found that this device can measure motor agility under constant loading, and the index obtained under light loading correlates with the maximum tongue pressure during isometric contraction and negatively correlates with the OD rate results.
This paper addresses to clarify the contribution of a mass property of a rigid and small subsystem to low order resonance frequencies of a whole structure. Based on both a Frequency Response Function (FRF) based sub-structuring and a kernel compliance analysis, it is expected that the control of mass properties of a subsystem may dominates relatively low order resonance frequencies of a whole structure. Our proposed method decomposes, at first, a whole structure of interest into two different sizes of subsystems. In this decomposition, a small subsystem only is subjected to structural modification. Since the FRFs on interface DOFs of these two subsystems, based on the insight by the kernel compliance analysis, dominate the resonance frequencies of a whole structure, the FRFs on interface DOFs of the small subsystem have also a critical role. However, in the frequency range of low order resonances of a whole structure, the FRFs of a small subsystem is simply dominated by rigid body modes and have no resonance. The FRFs of a small subsystem in this frequency range are, therefore, dominated by a mass property of a rigid and small subsystem. The paper proposed that the effect of the mass properties of a rigid and small subsystem on the low order resonance frequencies can be visualized using a Gershgorin diagram, and the low order resonance response of interest can be reduced by optimizing the mass property based on the visualization by detuning the resonance frequencies from dominant excitation frequencies. Finally, this paper shows that it is possible to control low order resonance frequencies of a whole structure by changing the mass properties of a rigid and small subsystem using the visualization of Gershgorin circles through a concrete numerical example.
Although an individual carbon nanotube (CNT) has superior thermal property, it is known that the property is deteriorated when forming CNT-based bulk materials such as film and fiber. To resolve the issue, encapsulation of materials into an inner space of CNT has been considered. Encapsulated material usually plays the role of scatterer for phonons and then suppresses heat conduction. However, the influence of encapsulating material on heat conduction is not fully understood. Thus, exploration of encapsulated materials for improving thermal conductivity is demanded. Graphene nanoribbon (GNR) has inherently high thermal conductivity and it can be used to enhance heat conduction of CNT-based bulk material. However, a previous experiment observed a twist of GNR encapsulated in CNT and this twist may negatively influence heat conduction. By using a combination of atomistic Green's function and mode-matching methods, we here investigate the impacts of a single twist and series of twists on phonon transport inside a GNR. As for the single twist, we found that the thermal conductance linearly decreases with increasing specific twist angle (twist angle per unit length). Furthermore, we found that phonons with long-wavelength longer than a length of twisted GNR are largely impeded and geometrical scattering is dominant. On the other hand for series of twists, although mutual interferences of phonons scattered by twists were expected to reduce overall heat conduction, it is found that a single twist mostly determines heat conduction, and thus non-local effect on phonon transport is negligible.
Mobility scooters are three or four-wheeled electric-motor-driven wheelchairs with a handlebar for steering. In the use environment of a mobility scooter, there may be many obstacles that need to be avoided, such as pedestrians on a narrow sidewalk or cars on the edge of the road. These obstacles not only interfere with smooth driving but also induce mental strain on the user such as fear and anxiety, which may cause a decrease in comfort and an accident. The purpose of this study is to estimate physical obstacles in the road environment when driving a mobility scooter from operation information and physiological information of the user obtained during driving. We measured skin conductance, manipulation amount of accelerator, steering torque, and acceleration value in the horizontal plane when driving on a few courses with physical obstacles. We tried to build a machine learning model that estimates the type of physical obstacles in the course based on these time-series data by using a random forest classifier.
A direct-lubrication tilting pad bearing with a diameter of 120mm is tested to clarify the effect of the oil flow rate on the characteristics of the bearing. Measured characteristics are the bearing temperature and dynamic characteristics, namely, bearing stiffness and damping coefficients. The applied load and the peripheral speed, as well as, oil flow rate are changed. The higher the oil flow rate is, the lower the bearing temperature is. At the specific load of 1.0 MPa and the peripheral speed of 90 m/s, the bearing temperature at the oil flow rate of 14 L/min is 102 ℃, while it is 83 ℃ at 42 L/min, and the difference is as much as 19 degree centigrade. Dynamic characteristics measured are also variable with respect to the amount of oil flow rate. The lower the oil flow rate is, the lower the damping coefficients are. As for stiffness, the values at oil flow rate of 14 or 28 L/min can be lower or higher than that at high oil flow rate of 42 L/min.
In order to create an inexpensive micrometer-sized plastic asperities, a polyvinyl chloride solvent dissolved in acetone was prepared so that the solvent droplet was put on silicon substrate and placed between parallel plate electrodes (the gap was 5 mm). The effects of concentration, DC/AC and their combination voltage on the creation of micrometer-sized plastic asperities were clarified. As a result, asperities with a height of more than 10 μm were observed from a solvent concentration more than 2.51 mg/ml. It was found that the asperities height increased linearly from around 10 μm to 14 μm with the applied voltage of 0.1 kV to 2.0 kV between the parallel plate electrodes. The effect of DC or AC of 2.0 kV on asperities height and number per unit area were conducted, then the height of asperities decreased from 14 μm to 10 μm when frequency was applied to 11 Hz. To confirm the effect of applying AC voltage on motion of the solvent droplet, high-speed camera observation was carried out. It was revealed that the droplet oscillated by applied AC voltage between parallel plates. The dimensionless height of the droplet increased and reached a maximum at AC 11 Hz. Finally, to clarify the effect of the initial voltage application method on the formation of asperities, a voltage was applied between the parallel plate electrodes under the conditions of DC/AC and no voltage for an initial evaporation time of 3 min. By applying AC 11 Hz during solvent evaporation period, it was clarified that the asperities dispersed most on the surface, then variations in asperities height were reduced.
In the grinding process, the difference of the grinding wheel surface condition affects a grinding performance and a ground surface roughness. It is well known that the grinding wheel surface topography is changed by the difference of dressing condition and the self-sharpening. Therefore, to estimate the optimal dressing conditions and/or manage the grinding wheel life, it is required that the relationship between the grinding wheel surface topography and the grinding characteristic is clarified. From such a viewpoint, by the proposed measuring method called a measured focus position recalculation method, the grinding wheel surface shape is measured before and after dressing and groove grinding. This study aims to quantitatively evaluate the relationship between the grinding wheel surface topography, grinding force and ground surface roughness. From experimental results, by extracting only the changed part of the grinding wheel surface shape before and after dressing and groove grinding, it was found that changes in the grinding wheel surface could be evaluated. Moreover, the abrasive grain cutting edge density, the abrasive grain contact area ratio and the successive cutting-point spacing were calculated by measured results of the grinding wheel with dressing lead changed. By these calculated results, it was clarified that the effect of the grinding wheel surface topography of the difference of dressing lead could be evaluated quantitatively. Finally, it was experimentally clarified that the normal grinding force had the same tendency as the contact area per abrasive grain cutting edge, the ground surface roughness had the same tendency as the successive cutting-point spacing.
LFV is one of effective machining technologies to break long and continuous chips in the turning process. LFV technology stands for low frequency vibration cutting. Vibration in the tool feed direction is applied in LFV and it is synchronously controlled with the spindle rotation. When the machined surface is focused on, characteristic surface patterns are formed in LFV turning process because of the tool vibration in feed direction. In this paper, a simulation technique to visualize the surface profile generated on the cutting process with LFV was developed. By visualizing the surface shape and contour shape, it is possible to clarify its features and calculate the surface roughness and roundness. During LFV operation, unlike conventional turning with constant feed rate, a cutting edge moves on the machined surface while vibrating in feed direction; hence characteristic patterns are formed by the uncut portion corresponding to the crossing cutter marks depending on the vibration conditions. The influence of such characteristic patterns on the surface roughness and the contour profile was clarified in detail. In addition, the vibration condition which can minimize roundness of the machined object was identified by using the developed simulation. Then the contour profile of the machined parts during LFV operation could be controlled.
Cell migration is critical in many physiological processes, including morphogenesis, wound healing, and metastasis of cancer cells, and thus elucidation of the mechanism of cell migration is quite important. It is well known that these processes of cell migration can be guided by microenvironment of the substrate surfaces, such as microgrooves. However, detailed mechanism of cellular mechanical sensing for microgrooved surfaces has not been clarified yet. Here we investigated the migration responses of cells on the microgrooved substrate in consideration of the effects of cell type differences. We cultured vascular smooth muscle cells (VSMCs) obtained from different animal species (porcine aortic smooth muscle (PASM) cells and rat aortic smooth muscle (RASM) cells) and cervical cancer cells (HeLa) on the microgrooved substrate with 2-μm groove width and approximately 200-nm groove depth, and assessed the shape changes and migration behavior of the cells. Both types of VSMCs migrated directionally on the microgrooved substrate, but their detailed responses were quite different: PASM cells became more elongated shape on the microgrooves while maintaining their adhesion area and exhibited marked directional migration on the grooves. In contrast, RASM cells showed a significant reduction of adhesion area on the microgrooved substrate and they occasionally locomoted obliquely on the grooves. Interestingly, HeLa cells did not elongate in their shape on the microgrooved substrate with random migration direction, indicating that HeLa cells could not sense the microgrooved surfaces. These results indicate that the changes in cell shape and migration behavior might be dependent on the difference in intracellular structure due to the cell type differences, and these differences can be emphasized by the culture on the microgrooved surfaces.
Our research aimed to develop algorithms to evaluate the quality of karate motions. Kata is the representation of karate’s self-defense techniques strung together into a performance routine. Kata is judged based on several technical and physical criteria including speed, strength, focus, breathing, balance, and rhythm. For this reason, evaluation of karate motions is challenging. In this research, we created a novel dataset of referee scores and inertial sensor data of karate movements. The subjects were 22 members (15 males, seven females, age 20 ±1.3 years) of Waseda University’s Karate club who competed at the international and regional level. Inertial sensors were attached to five body parts (forearms, lower legs, and waist) and the subjects performed fundamental movements in karate (reverse punch, upper level block, and front kick) as the target actions. Subjects performed 30 trials for each action. The quality of each action was scored by an official referee as the ground truth. Also, the quality of each action was scored by subject's self-assessment as the comparison. The resulting data was distributed into the learning dataset and the evaluation dataset. Next, we developed a classifier that evaluates the quality of each action in the learning dataset in three stages. First, the importance of each feature was judged using ensemble learning. The classifier then evaluated the karate motions using handcrafted features of high importance. Finally, the classifier constructed strong classifiers by combining weak classifiers. As a result, our evaluation method was applied to the test dataset. The matching rate of the estimated value and the ground truth was 0.830 ± 0.067 (Mean ± SD). Also, the accuracy of self-assessment was 0.504 ± 0.039. Also, there was significant difference at the 1%.
The cells in living tissue change not only their proliferation and motility, but also their mechanical properties in response to external mechanical stimuli. The mechanical properties of the cells and their adhesion strength with the extracellular matrix are extremely important for understanding cellular mechanotransduction mechanism and in regenerating of load-bearing biological tissues such as blood vessels, bones, and ligaments. On these backgrounds, a micro tensile tester for investigating the mechanical properties of isolated cells was developed in our laboratory. However, the tester required many manual operations for force-deformation analysis resulting a large time consumption. Therefore, in this study, we developed a micro-tensile tester capable of in situ measurement of force applied to the cells and their deformation by using image-based real-time analysis for the deflection of a glass micro needle attached to the specimen cells. Using this tester, we measured the tensile stiffness of cervical cancer HeLa cells and their adhesion strength to the substrate. We found that the tensile stiffness and adhesion strength of HeLa cells were approximately 1/4–1/5 of the reported values of vascular smooth muscle cells, indicating the structural differences in the both types of cells. This finding strongly indicates that the whole cell mechanical properties, adhesion forces, and intracellular structures in cancer cells are deeply involved in their physiological functions, including migration in a narrow space and further division and proliferative ability.
Coupled loads analysis (CLA) has been used in order to evaluate structural design of satellite for vibration environment during launch and micro-vibration disturbance environment on-orbit. Each time the design of satellite’s substructure is updated, CLA, which is to calculate coupled vibration responses by using coupled whole model, needs to be performed. In the case of frequently re-calculation, CLA is not an efficient means due to its costly calculation caused by coupling of updated models, defining forcing function and managing and assessment re-calculation result of finite element analysis. Therefore, there is a need for a method for efficiently calculating coupled vibration responses. In this paper we propose a quick update method of coupled vibration responses to evaluate updated design efficiently without the costly calculation. In the proposed method, the initial accelerations at the boundary of substructures without coupling of them are once calculated, and then the initial boundary accelerations can be updated to the coupled boundary accelerations by simple matrices calculation using Craig-Bampton model parameters of substructures. We show a calculation example of the proposed method with simulation models, which demonstrates that the coupled accelerations calculated by the proposed method correspond well with those of finite element analysis results.