We developed a semiconductor strain sensor chip for measuring the biaxial strain with high sensitivity and low power consumption. This sensor chip has two bridge circuits (sensors) that consist of an impurity diffusion layer on a silicon substrate, and are arranged perpendicularly to each other. High sensitivity gauges and low sensitivity gauges in the chip are n-type and p-type diffusion layers, respectively. We performed a tensile test with a test piece, to which the developed strain sensor and a strain gauge were attached. We measured the strain sensitivities for each axis of the sensor. The strain sensitivities of the longitudinal and vertical directions were -12.4 and 4.9, respectively. The developed strain sensor was applied to the measurement of biaxial strain in the biaxial strain field and compared with the theoretical value and strain gauge measurement. We confirmed that the measured strain value of the developed strain sensor coincides with the theoretical value within 10% and it coincides with the measured value of the strain gauge within 8%.
A mechanics-of-materials deflection analysis of wooden baseball bats at impact is developed. Consider the bat which is simply supported a point of grip and elsewhere free to rotate, and the bat is subjected to the impact force with ball and the inertia force due to the sudden change of the angular velocity in swing. The static force balance gives the relation between the impact force and the inertia force, but the magnitude is left undetermined. By assuming that the impact duration is 1 ms, we get the solutions of the energy conservation equation as a function of hitting point. The present model provides the evidence for the COP (center of percussion) to be located very close to but not exactly in the sweet spot where the kinetic energy of bats can be most effectively transferred to the outgoing velocity of batted ball. Additionally, the deflection analysis determines the bending stress imposed at given velocities of bat and ball. It is shown that the largest bending stress is always located at the top of grip length irrespectively to hitting point. One hundred fifty broken bats in Hokkaido University play fields were collected and fracture surfaces were examined.
In the present study, we propose a new repulsive layer model in order to establish Brownian dynamics simulations for cube-like particles, although various repulsive layer models have been proposed by other researchers. In order to verify the validity of Brownian dynamics simulations with this repulsive interaction model, we address a suspension composed cubic hematite particles in an equilibrium situation. The results obtained here are summarized in the following. In the case of the ordinary model by Donaldson et al., the accuracy and the CPU time of simulations are significantly dependent on the number Nsph of spherical particles filling up one side of cube-like particle. As the value of Nsph is increased, the simulation time becomes more prohibitive although we can expect to obtain more accurate results. From the comparison in respect to the results of the orientational correlation function, we understood that the model with Nsph=3 exhibits quite different results in comparison with Monte Carlo results. This is because the corners and sides of the cubic particles cannot be modeled with sufficient accuracy in the case of Nsph=3. On the other hand, the model with larger values of Nsph tends to give rise to better agreement with Monte Carlo results. We may therefore conclude that the model of Nsph=5 or Nsph=7 should be used in order to obtain simulation results with sufficient accuracy if using their repulsive moled. In the case of our model, the simulation time corresponds to their model of Nsph=3, and the accuracy of simulation results is very similar to that for the models of Nsph=5 and Nsph=7. If considering the simulation time and the accuracy of the simulation results, we may conclude that our model has more significant advantage to the ordinary models in simulations for a suspension of magnetic cube-like particles.
During polymer melt extrusion from a circular nozzle, the extrudate at low flow rate shows a stable linear shape with smooth surface but the extrudate at higher flow rate shows unstable shapes with spiral, rosary, or zig-zag structures. This phenomenon is known as melt fracture and hampers high throughput production in polymer processing. For linear polymers, synchronized oscillation of flow volume, extrusion pressures, and shape distortion is frequently observed, and it is known as stick-slip melt fracture (SSMF). Since this phenomenon is an oscillation phenomenon, many studies have been performed to analyze the mechanisms based on the oscillation theory. However, most of previous studies have mainly used mathematical calculation, and therefore experimental evaluations of SSMF have rarely been performed. In this study, we conducted an experimental approach to elucidate the mechanism of SSMF by using high density polyethylene as a polymer with varied lengths of the extrusion nozzle. Experimental results were analyzed by the simple model based on the oscillation theory. In the model, we introduced a supply curve representing a relationship between flow rate and pressure at the supplying side and a flow curve representing a flow resistance at the nozzle side. As a result, it was clarified that SSMF is a phenomenon of self-exited oscillation and also relaxation oscillation caused by the compressive elasticity of polymer melt and the negative damping appearing in a flow curve. We verified that SSMF does not occur when the negative damping is lost by repressing slip at inner side of the nozzle. Furthermore, we identified conditions under which SSMF does not occur despite the existence of negative damping; occurrence of SSMF depends on the mode of polymer supplying, a constant flow mode or a constant pressure mode. The former causes SSMF but the latter does not.
If road surface friction coefficient can be measured in real time, the performance of various vehicle control systems such as ABS (Antilock Braking System) and automatic braking systems can be improved. Therefore, many studies measuring road surface friction coefficient from strain in the bottom of a tire, which is inside of the tire tread and is the only part in contact with a road surface, has been done. However, a sensor installed on the bottom of a tire is easy to peel or damage because large deformation occurs locally on the bottom of a tire by rugged road surface. The authors studied a method of measuring road friction coefficient from strain induced in the tire sidewall. If the strain in the tire sidewall is used, stable measurement is expected because the tire sidewall is harder to deform locally than the bottom of a tire. First, we measured the relationship between vertical and horizontal loads acting on a ground contact surface of a tire and strain induced in the tire sidewall. Second, we established experimental formulas that can express these relations and methods of measuring road friction coefficient. Third, we confirmed that the proposal method can measure road friction coefficient at various ground planes with sufficient accuracy.
This paper proposes a structure and a measurement method of a very small range image sensor for short distance measurement using a multi-slit laser projector. In recent years, industrial robots used in production lines have become widespread, and development of humanoid robots that operate in the same environment as humans is also proceeding. Many of these robots have an arm mechanism for gripping an object. In order to grasp an object, it is necessary to measure the distance and the object, so these robots are equipped with range image sensors. However, if the position of the range image sensor is away from the arm end, occlusion occurs by the arm during the gripping operation, and the object to be gripped cannot be measured. Therefore, a very small range image sensor that can be attached to a robot hand is required. The sensor used in this research projects multi-slit laser and measures the distance by the disparity of the detected laser light. For measurement, it is necessary to identify the number of each slit laser. Therefore, for the discrimination, the intensity information of the laser light image is used. The effectiveness of the proposed sensor is verified through short-range object measurement experiments.
In this paper, we proposed a new particle method for numerical simulation of droplet dynamics. In the proposed method, the moving surface mesh is used to define interface between gas and liquid. The volume enclosed by the mesh represents the liquid droplet, and the outer domain is inactive gas with constant pressure. The incompressible liquid flow is calculated using a particle method, in which spatial derivatives are evaluated using an arbitrary high order accurate scheme. On the free surface, the surface stress balance equations, including surface tension and viscous stress, are adopted for the boundary conditions. Deformation of the gas-liquid interface is explicitly calculated by surface nodes that move in a Lagrangian fashion. Surface tension force is directly evaluated with high accuracy on each node utilizing the mesh shape. As numerical verification, simulations of three benchmark problems, namely circular patch test, Laplace pressure test and 2D droplet (liquid column) oscillation problems with different oscillation modes, have been carried out. The computation results were compared with the theoretical solutions, and excellent agreements were obtained. As a result, high accuracy and validity of the proposed computational method were confirmed.
This paper aims to develop a scheme for geometrical feature constraints in topology optimization for Additive Manufacturing (AM) without support structures based on the Partial Differential Equation (PDE) of geometrical shape features. To begin with, the basic concept of topology optimization and a level set-based topology optimization method are briefly described. Second, the PDE system for geometrical shape features is formulated. Here, aspects of the distribution of state variables are discussed using an analytical solution of the PDE. Based on the discussion, a function indicating the extended normal vector including geometrical singularity points is formulated. Third, geometrical requirements of product shape in AM without support structures – the so-called overhang constraint – are clarified in two-dimensions. A way of extending of the proposed concept to three-dimensional problems is also clarified. Additionally, geometrical singularities in the overhang constraint are discussed. Based on the PDE system and the clarified geometrical requirements, the overhang constraint including geometrical singularities is formulated. A topology optimization problem of the linear elastic problem is formulated considering the overhang constraint. A level set-based topology optimization algorithm is constructed where the Finite Element Method (FEM) is used to solve the governing equation of the linear elastic problem and the PDE, and to update the level set function. Finally, two-dimensional numerical examples are provided to confirm the validity and utility of the proposed method.
We attempt to construct a novel technology development utilizing big data such as Deep Learning in the manufacturing industry. Especially, we look at the data mining method and the tool catalog as a useful big data base which is updated by tool makers because it is easy for CAD/CAM engineers and machine tool operators to obtain it in the manufacturing fields. In the present report, we proposed the visualization and consideration of cutting condition determination process based on a decision tree method which is one type of statistical analysis method for radius-endmill data base. We also developed a cutting condition prediction system with a random forest which is a type of machine learning method applying a decision tree. Moreover, we performed a case study in endmilling under deriving cutting conditions by the proposed method, which is an unknown and expanded cutting condition based on tool catalog data base. As a result, it is demonstrated that the support based on machine learning is found to be effective to select a cutting condition including an unknown cutting condition in tool catalog data base.
The purpose of this study is to investigate the gait improvement for patients after total hip arthroplasty (THA) by using accelerometers attached to the trunk of body before and after surgery (initial gait after THA, in hospital, at discharge, 3 months after THA, 6 months after THA, 1 year after THA). Thirty patients (mean age 61.1 ± 11.1 years old) were selected. Twelve healthy subjects (mean age 24.1 ± 2.6 years old) were also selected as a control group. Dynamic load factor (DLF) corresponding to the vertical walking force and lateral displacement of the trunk are calculated using power spectrum density for time history trunk signals measured by the accelerometers. The parameter PR in the fore and posterior directions is also obtained which is defined as the power spectrum ratio of 0.5fw to fw component where 0.5fw is half frequency component of the gait cycle fw. Based on these results, it was confirmed that the parameter PR in the fore and posterior directions, DLF in the vertical direction and lateral displacement of the trunk were the useful evaluation indices in order to evaluate the gait improvement for THA postoperative patients.
In rubber baseball games, when the rubber ball is hit by a baseball bat, the rubber ball is deformed greatly comparing to an official baseball ball, and the batted ball speed decreases due to the energy loss during the deformation. Since the new rubber ball has been applied in games from 2018, the material properties and the restitution characteristics of the new rubber ball attract plenty of attention among scholars. In this study, the difference of the material properties and the restitution characteristics between the new and old rubber balls is investigated deeply by the static compression and collision tests. According to the static compression test, we find that the new rubber ball is harder and more difficult to generate deformation than the old one. In the collision test, the rebound ball speeds of both of the new and the old balls become faster when using a smaller diameter of steel cylinder instead of baseball bat, and the rebound ball speed of the new ball is slower than that of the old one under the same experimental conditions. Furthermore, to develop high performance baseball bats adapting to the new rubber baseball, the diameter of the baseball bat is studied by the impact simulation based on the finite element analysis. In the simulation, the batted ball speed under the analytical conditions of different offset heights and different barrel diameters of the bat are evaluated considering the initial spin. As a result, the batted ball speed generated by the bat with diameter φ55 mm is faster than generated by the bat with diameter φ70 mm when the offset height range is smaller than 14.6 mm, so that the bat diameter φ55 mm is recommended according to the present work.
This paper presents examination of a proposed method for center of gravity (COG) velocity estimation during walking using information obtained from lower limb motion measurements. Lower limb joints and muscles around these joints are used during walking. Gait velocity changes according to lower limb muscle activity. Some earlier reports of relevant studies have suggested that lower limb muscle weakness reduces the walking rate, which increases the probability of falling. Therefore, the relation between the COG velocity and lower limb motion during walking must be clarified. For this study, we constructed gait COG velocity models that represent the relation between the COG velocity and lower limb joint power for each gait phase. For this experiment, gait was measured using a 3D motion analysis system and floor reaction force gauges. We estimated the gait COG velocity models’ parameters by applying Kalman filtering using measurement information. The results of analyses using gait COG velocity models indicate a quantitative relation between the COG velocity and the lower limb joint power during walking. Furthermore, results demonstrated that the lower limb joint power that influences the COG movement differs in each gait phase. This analytical method is anticipated for use in the evaluation of healthy feet and ill feet and for evaluating the balance of left and right feet.
Center of pressure (COP) has been one of the most popular index for balance evaluation in quiet standing. However, the balance evaluation based on COP has been limited due to its accuracy. For accurate balance evaluation, an estimation method of the center of mass (COM) from simple measuring devices is desirable. The purpose of this study is to estimate COM on sagittal plane from force plate measurement. One of the most popular method suggested in past studies is to integrate the COM acceleration estimated from shearing force on support surface, however, this technique requires appropriate boundary conditions. Instead of the integration method, we adopted a COM estimation method via gravity term in equation of angular motion. While the method can estimate COM in real time, an estimation error arose from the assumption of a single rigid body model. To clarify the estimation error in theory, we introduced a modal coordinate (rigid body mode and zero shearing force mode) in the analysis of double-link model. As a result, we found that the estimation accuracy decreases due to the influence of acceleration of zero shearing force mode. From a practical point of view, if the amplitude of COP and the ratio of zero shearing force mode is relatively small, COM can be estimated with high accuracy. Validation of the present method was verified by comparing COM from force plate measurement with that from motion capture measurement in stationary standing test and horizontally sway test.
A perforated plate is used as an acoustic absorption material for compressors and acoustic barriers for roads and railways. The effects of the perforated plate on the acoustic natural frequency of an one dimensional sound field partitioned with the perforated plate has been studied in our previous investigations. And it was clarified that the acoustic natural frequency of the one dimensional sound field partitioned with the perforated plate becomes lower as the aperture ratio becomes smaller. There are two methods obtaining the acoustic natural frequencies. One is the method based on the eigenvalue analysis. And the other is the one based on the peak frequency of the response analysis. In this paper, the impedance derived by Melling is used for the response analysis. we compared two acoustic natural frequencies calculated by different two methods. As a result, it was clarified that the acoustic natural frequency calculated by the response analysis was a little smaller than that calculated by the eigenvalue analysis in all conditions. But its difference is small, and both the acoustic natural frequencies calculated by two methods agree with experimental results. And it has become easier to physically understand the analytical and experimental results by considering and comparing the element of transfer matrix.
The icing phenomenon, which is due to continuous deposition of water droplets or super-cooled droplets, causes serious problems, such as airplane crashes and power line tower collapse, in various fields. It is important to understand the fundamental icing process to overcome these problems. In this study, a free-fall drop test was conducted to investigate the effects of substrate temperature and falling height on the deposition process for a water droplet. A water droplet with a temperature of 20°C was freely dropped onto an A2017 aluminum alloy substrate, which has been cooled to a temperature between -20°C and -70°C, from a height of 600, 800, or 1000 mm. The deposition process was continuously observed via a high-speed video camera. Consequently, cracking occurred in solidified droplets at substrate temperatures below -22.5°C. In addition to cracking, partial delamination of a solidified droplet from the substrate was also observed to occur at substrate temperatures below -32.5°C. These critical temperatures were independent of the falling height. Theoretical prediction models were established to predict these critical temperatures, variation of the water droplet diameter during deposition, and the time required for crack initiation. The validity of the established models was demonstrated via comparison with the experimental results.
The control of the imbalance of wheel load in a railway vehicle is important in maintaining running safety against a flange climb derailment. This paper discusses a control method for quasi-static wheel load variation in transition curves by utilizing the leveling devices that are widely installed on recent railway vehicles with air suspentions. We propose a hardware construction to control wheel load variation by using pneumatically controllable leveling valve rod, of which the length is adjustable by using pneumatic cylinders. We also propose an in-vehicle control method, which means that the control method does not depend on the relative position between the vehicle and the earth (e.g. GPS) explicitly. We confirmed that 30% of wheel load inbalance is reduced at its maximum by appling the proposed control method in a transition curve through a running test by the use of a real railway vehicle.
This study proposes the efficient error rate estimation method for Single Event Effects (SEE) considering statistical uncertainty. SEE is known to make significant damage to a semiconductor device used for a spacecraft on orbit by exposed to cosmic rays or high energy protons. Semiconductor devices for the spacecrafts must conduct various ground experiments to evaluate the error rate using several environment simulators. Since the ground experiment takes much cost and time, the number of experimental samples is limited. That makes it difficult to estimate the error rate with high accuracy. That is, effect of statistical uncertainty due to the small number of samples on the error rate estimation should be considered. Therefore, this study proposes the highly accurate estimation method by introducing a prior distribution update into Hamiltonian Monte Carlo method (HMC) that is one of Malkov Chain Monte Carlo (MCMC) methods considering effects of statistical uncertainty. Through numerical calculations, the validity of the proposed method is illustrated.