In this study, the notch strength σBnotch was investigated for high silicon solid solution strengthened ferritic ductile cast iron in comparison with the tensile strength σBsmooth. High speed tensile tests were conducted on notched and smooth specimens at various strain rate and temperatures. The strain rate-temperature parameter (R parameter) is found to be useful for evaluating the temperature and strain rate upon the notch strength. The required range of R parameter was investigated for welded structural members in several industrial fields. The notch strength σBnotch is always larger than the tensile strength at room temperature σB,smoothRT in the range of R parameter required for the welded structures. Therefore, tensile strength σB,smoothRT is confirmed to be more useful than Charpy absorbed energy for the structural design. It is expected that the high Si ductile cast iron has wide industrial application potentiality.
This paper presents experimental, analytical and numerical study of impact perforation of steel plates with the aim to develop the procedures to assess the perforation of steel against tornado-generated missile impact. In the experiment, flat plates of SS400 steel and SUS304 stainless steel were perforated by a square pipe with cross section 200 x 300. Projectile mass and impact velocity were kept constant, namely, approximately 1300 kg and 17 m/s. Perforation limit thickness of SS400 and SUS304 flat plate was determined to be 9 mm and 6 mm, respectively. BRL formula was used for the analytical study, and equivalent diameter of square pipe for BRL formula was defined based on the experimental data. Numerical simulations of some experiments were also carried out and the effect of thermal softening and stress triaxiality on failure strain have to be taken into account in the material model in order to reproduce the experimental results.
Fatigue properties of the thick carbon fiber reinforced plastic (CFRP) laminates with toughened interlaminar layers in the out-of-plane direction (Z direction) and in the in-plane transverse direction (T direction) were evaluated experimentally. Spool specimens were machined from the thick mother plates which were laminated prepregs of T800S/3900-2B unidirectionally. The specimens were attached to metal tabs to apply loads in the thickness direction of the specimen. The tensile strengths in Z and T direction were measured by static tensile tests and S-N curves were obtained by fatigue tests at a stress ratio of R=0.1. As the results, the tensile strength in Z direction was 24% lower than that in T direction. Fatigue strength in Z direction at 106 cycles was also 25% lower than that in T direction. It was observed using a digital microscope that the fracture occurred in intralaminar layers in both static tensile tests and fatigue tests in Z direction. The thermal residual stress which was generated during the fabrication process and the stress distribution by mechanical loadings in spool specimens were calculated by finite element analysis. The calculated results showed that compressive residual stress applied in intralaminar layers in T direction by restraining the thermal deformation. It is found that the static tensile and fatigue properties in Z direction were almost the same as those in T direction by evaluating with the stresses applied in the nearest intralaminar layer to the minimum cross-section in the spool specimen.
Titanium and titanium alloys have a lot of excellent characteristics when used for the parts and components of machines and structures. As for bolted joints, however, they are used only for some limited cases because of the high cost. Their specific characteristics, e.g., low weight and high resistance to corrosion, are highly attractive from the engineering point of view. In this paper, thermal contact coefficients at the interface composed of titanium and titanium alloys are measured, and the empirical equations for evaluating the coefficients are derived in the same form proposed in the previous papers. Then, heating experiments of bolted joints, tightened by titanium bolts, are conducted to examine how the bolt preloads vary when subjected to thermal loads, and the bolt preload variations are compared to the case tightened by carbon steel bolts. In the next place, aiming at a broader use of titanium and titanium alloy bolts, numerical analyses are performed to demonstrate the effectiveness of those bolts by incorporating the foregoing thermal contact coefficients into the finite element formulation. The numerical results are favorably in good agreement with the experimental ones, and they suggest that threaded fasteners made of titanium alloys can be favorably applied to the joints whose clamping forces are likely to decrease when subjected to thermal loads.
High-speed tensile testing is now being recognized as a standard testing method for evaluating the impact strength of engineering materials. The impact speeds of Izod and Charpy tests cannot be controlled and therefore do not correspond to the real failure of real products. The brittle-ductile transition of structural materials is affected by the temperature and loading speed. In the high-speed tensile test, it is necessary to obtain the strain rate at the notch root accurately to understand the effect of impact load. For smooth specimens, the strain rate can be determined from the tensile speed u/t and specimen length l as εsmooth = u/tl. For notched specimens, however, the strain rate at the notch root εnotch should be analyzed accurately. In this study, therefore, the strain rate concentration factor defined as Ktε = εnotch/εsmooth is studied with varying the notch geometry. To predict the strain rate concentration factor Ktε accurately, the relationship between Ktε and the stress concentration factor Kt* = σmax/σgross is investigated. Here, σgross is the remote tensile stress and P is the tensile load. It is found that the strain concentration factor Ktε can be estimeted from stress concentration factor Kt* when the relative notch depth 2t/D≦0.5 (t : notch depth, D : the specimen diameter).
In this study, the effect of shot peening on rolling contact fatigue life of bearing steel was investigated under contaminated lubrication. Shot peening was carried out on bearing steel SUJ2 specimens. Peened specimens were polished to remove the dimples generated by shot peening. The distribution of Vickers hardness and residual stress of the specimens were measured before and after the shot peening. The resistance to indentations was compared by examining the profile of the Vickers indentations. Then, rolling contact fatigue tests were carried out under contaminated lubrication. The material hardness was improved up to about 100 HV on the surface to a depth of 300 μm, and compressive residual stress was generated up to 1546 MPa at a depth of 25 μm due to the shot peening. In addition to the width and the depth of the Vickers indentation, the ridge height which causes the stress concentration around the indentation, was reduced by 17% by the shot peening. The rolling contact fatigue life associated with a 50% reliability (L50) was improved 62 % by the shot peening. However, the improvement of rolling contact fatigue life associated with a 90% reliability (L10) was only 26 % because of the increase in dispersion of the fatigue lives due to surface cracks created by the shot peening. Based on the present result, the increase of surface hardness and generating the large compressive residual stress near the surface by shot peening was found to be effective in increasing the rolling contact fatigue life in contaminated lubrication.
To improve the high-temperature oxidation resistance of grade S45C carbon steel, we formed a Cr / Ni diffusion layer on the surface of carbon steel by atmospheric-controlled induction heating fine particle peening (AIH-FPP) treatment. Cr and Ni particles were mechanically milled in planetary ball mills and used as shot particles in the AIH-FPP treatment to create a Cr / Ni diffusion layer. High temperature oxidation tests were carried out at 900°C for 100 hours to evaluate the high-temperature oxidation resistance of the AIH-FPP treated specimen. The mechanically milled particles and specimen were analyzed using a scanning electron microscope, an energy dispersive X-ray spectrometer, and an X-ray diffractometer. Results show that the AIH-FPP treated specimen prepared using mechanically milled particles formed a Cr / Ni diffusion layer on the carbon steel. The carbon steel sample with the Cr / Ni diffusion layer exhibited improved high-temperature oxidation resistance compared to the untreated sample. This is due to the formation of Cr and Ni oxidized layers on the treated surface, which inhibited oxidation of the inner substrate. The results indicate that a Cr / Ni diffusion layer formed by AIH-FPP treatment using mechanically milled particles can improve the high-temperature oxidation resistance of grade S45C carbon steel.
Shot peening is widely applied in the automotive and aerospace industries in order to improve the fatigue strength of the metal components by compressive residual stress. In the case of large components, the peening process is generally performed by moving peening equipment that follows a trajectory on the component surface by means of a robot. In order to construct a robot program for the shot peening of complex components, this study aimed to obtain a functional approximation of the impact pressure distribution in the shot stream. The impact pressure distributions were measured with pressure measurement films (Prescale) and a pressure distribution mapping system. The dependence of the mean impact pressure in the shot stream on the shot mass was in good agreement with the dependence of the arc height of the Almen strip on the shot mass. The impact pressure distributions using various shot masses and standoff distances were measured and approximated by modified Gaussian distribution functions, which included the saturation curve. Three coefficients in the modified Gaussian distribution functions depended on the shot mass and the standoff distance. The modified Gaussian distribution functions were used to determine the impact pressure distributions of a twice-shot peened samples. These calculated values were in good agreement with the experimental results. However, for tilted shot peening, the impact pressure distributions were more complex because the standoff distance at each position on the film was different. The impact pressure distributions of the tilted conditions calculated by the modified Gaussian distribution function, which considered the variation in the standoff distance, were in good agreement with the experimental results for a tilt angle ranging from 30° to 90°.
Recently, the refrigeration air conditioner and heat pump system using the two-phase flow ejector is beginning to appear, as the efficiency of the ejector cycle is improved largely in comparison with the conventional system. Shock and expansion waves can occur in the internal flow fields of the ejector, and the effect of the pressure fluctuation by those waves must be considered on the designs of the ejector. In this study, the pressure fluctuation of the shock wave appeared at the outlet of the two-phase flow nozzle are measured in the HFO1234yf refrigeration cycle. It was clarified by experiment that the amplification frequency components of pressure fluctuations are increased with the strength of the shock waves and the attenuation frequency components are increased with increase of liquid void fraction of downstream shock waves.
This paper describes how to exploit the elasticity and the dynamic coupling of a multi-link robot with elastic elements to improve the motion ability without depending on only actuator power. The focus is on swing motion (e.g., throwing or kicking motion) in this paper. The prime purpose of the swing motion is to increase the kinetic energy of an end-link (e.g., hand or foot). This paper proposed a method to generate a swing motion pattern for the increase of the kinetic energy of the end-link. In general, the multi-link robot has high-power actuators in the base side. The high-power actuators can produce a large amount of mechanical energy. Mathematical models were constructed to transfer mechanical energy from the base side toward the end side by exploiting the elasticity and the dynamic coupling. The swing motion pattern was generated on the basis of the models. The results of simulation experiments showed that the kinetic energy of the end-link increased explosively. The reason was that a large amount of energy produced by the actuators in the base side was transferred toward the end side.
To analyze the driving behavior is important for designing a comfortable automatic driving. So far, conventional PID models was widely used to steer the vehicle. It has been assumed that the driver looks at the constant point in conventional PID model. However, all drivers have experiences that the gazing distance changes according to the travel routes, driving situations and driver's characteristics. The PID gain of the steering model is assumed to be modified depending on driver's gazing distance. The facts are familiar, but the relationship between driver's steering gain and the gazing distance has not been clarified yet. If this relation becomes clear, it can be helpful for the comfortable driving assistance and/or automatic driving systems to provide for each driver. The aim of this study is to design a steering model estimated by Particle Swarm Optimization (PSO) depending on gazing distance . The feature of the model is on-line measurement of gazing distance incorporating the gazing distance explicitly into a model. The isolated driving and the following driving are evaluated using a Honda driving simulator. The effectiveness of the model is discussed individually.
In the present paper, development of an automatic spinach harvester is discussed. Our research group has been developing a prototype harvester and many filed tests have been successfully executed. The field test results show that spinach can be picked up automatically without being grasped after their roots being cut at specified position in soil. The harvester equips two degrees of freedom control units, such as the arm length control unit and the arm angle control unit, for controlling a root-cutting blade which follows the specified path under the ground. In the present paper, modeling and control design for the arm length control is discussed. First, a control design model is developed by several system identification techniques. Next, an I-PD controller is designed by the robust control design procedure. Control performance is verified by numerical simulations and field tests.
In this paper, we described the principle, design prototype and evaluation of of 3-dimensional gravity compensation mechanism for human coexistence robot. In this mechanism, it is possible to realize 3-dimensional gravity compensation by rotating the entire pantograph mechanism at the root and arranging actuators as counterweights so as to balance moments of all joints. We derive the relationship such as the link length and the center of gravity position to realize this. In addition, by constructing a mechanism that adds compensation force using wires, the entire arm is made as compact as possible. From the joint torque simulation and experiment of the prototype arm, it was confirmed that the arm can be driven with joint torque of 15% to 25% with respect to the arm without compensation meshanism. In addition, it was found that the effect of reducing the torque supporting the arm's own weight was larger than the influence of the increase of the moment of inertia by counterweight.
Immersive virtual reality system has a problem that the operability deteriorates if the shape of the virtual body is parted from the real body. The authors are assuming that this is caused by misfit of the body scheme, an internal model in the brain used to recall the body position, because it is initially tuned up to the real body instead of virtual body. Thus, the authors have proposed a method using VR technology called“ Body Scheme Calibration ”to change the body scheme adapting to the real body so as to fit the virtual body. However, in the previous approach, presented VR information was limited to visual information, and haptic information normally occurring from interaction with surrounding object was neglected. Therefore, this paper investigated the effect of haptic information on Body Scheme Calibration. As an experimental result, it was verified that the effect of additional haptic information is trivial, and the complex haptic interface for this calibration might be omissible.
We aim to clarify dynamics of the wrist turn of the golf swing and the effect of the parameters on dynamic behavior at the wrist turn using the double pendulum model and the modal analysis method. Eigenvalue analysis was carried out and natural frequency and mode were calculated by using linearized equation of motion assuming the exterior angle of the cock angle is small. We found out that the first mode is a rigid mode and the second one is a vibration mode of the double pendulum, and the mode shapes are constant during the wrist turn even though natural frequency changes. By applying the modal analysis method we obtained equations of motion for the rigid mode and the vibration mode separately. Furthermore, using the theory of linear superposition, the equation of motion for the vibration mode was separated again into 3 equations which can help to understand the mechanism of the wrist turn. After accuracy of the proposed method for small exterior angle of the cock angle was confirmed by comparing with the exact solution using numerical integration, the proposed method was applied to the general case with large exterior angle of the cock angle which has nonlinearity, and the mechanism of the wrist turn and the effect of the parameters of the arm and wrist torque on the dynamic behavior at the wrist turn were clarified qualitatively. Finally parameter survey using the numerical integration for the original nonlinear equation of motion was carried out to show the validity of the proposed method.
Vibration tests of the prototype of the newly developed three-dimensional seismic isolation mechanism were carried out using several real-scale three-dimensional seismic waves with the world's largest E-defense shaking table. The developed 3-D seismic isolation mechanism has an air levitation mechanism that isolates horizontal vibration and a spring link mechanism that isolates vertical vibration, in series. The air levitation mechanism floats only 50 μm from the floor and is in contact with the floor with a slight air viscous force of a friction coefficient of 1/1000. Since there is no spring force in the horizontal direction in this mechanism, there is no periodic motion and there is no amplification of vibration. Also, since the floating height is very small, the vertical rigidity is very high even in the air, and the rocking motion is not performed. The spring link mechanism combines a negative stiffness link and a positive stiffness link to minimize the spring stiffness. While maintaining the horizontal attitude by the link, a vertical natural frequency of 0.25 Hz was realized. The prototype showed unprecedented high performance of about 20 dB of anti-vibration capability at 1 Hz both in the horizontal and vertical directions, and the effectiveness was verified in this experiment. The seismic waves used for the experiment are the Takatori seismic wave of the Great Hanshin-Awaji Earthquake of 1995 and the Sendai seismic wave of the Great East Japan Earthquake of 2011.
This paper presents a method for analysis of motion of multibody systems. In the presented method, the null space matrix for the constraint Jacobian is determined by solving differential equations, not by solving algebraic equations which is common in other methods such as the coordinate partitioning method and the null space method. In the algorithm, the QR decomposition for the constraint Jacobian is utilized. Use of the differential equations for the null space matrix and the QR decomposition as well as the introduction of stabilization terms allow us to analyze without any problems motion of multibody systems which have redundant constraint and/or singular configuration. In addition, the presented method solves the Maggi's equation which is the equation obtained by eliminating the Lagrange multipliers from the equation of motion and by expressing the unknown variables only with the independent components. Thus the computational cost is not so high. The validity of the presented method is verified by numerical examples.
A flexible bag containing particles becomes rigid when the air inside the element is evacuated. Variable stiffness elements using granular jamming have been used for haptic displays and robotic orthoses helped by the soft and lightweight body. However, deforming variable stiffness elements causes wrinkles on the membrane, which decrease and destabilize the stiffness of the element. The wrinkles on variable stiffness elements are due to the non-stretchability of the outer membrane. A stretched membrane reduces wrinkles but decreases the stiffness of the element dramatically. This study suggests a wrinkle-free variable stiffness element with an outer membrane that is stretchable but rigid only when the air inside the element is evacuated. The amount of particles inside conventional elements limits the deformable range of the elements. On the other hand, the novel stiffness element can hold more particles without any loss of the deformable range, which increases the stiffness of the element. The stretchable outer membrane also reduces undesirable deformations of the element caused by wrinkles when the air inside the element is evacuated. The experimental results of this study confirm that the stiffness of the wrinkle-free variable stiffness element is greater and more stable than a conventional stiffness element.
Cymbals are percussion instruments that vibrate and radiate sounds when hit with a stick or when used in pairs. The sound radiated from a cymbal depends on its vibration characteristics. Cymbals are made through spin forming, hammering and lathing processes. The spin forming creates the domed shape of cymbals, determining the basic vibration characteristics. The hammering and lathing make specific sound quality adjustments by changing the vibration characteristics. In this paper, we focus on how the hammering affects the cymbal's vibration characteristics. The hammering produces many shallow dents over the cymbal's surface, generating residual stresses in it. These residual stresses change the vibration characteristics. We perform finite element analysis of the hammered cymbal to obtain its vibration characteristics. In the analysis, we use thermal stress analysis to reproduce the stress distribution and then with this stress distribution we perform vibration analysis. The results show that the effects of thermal load (i.e., hammering) vary depending on the mode: an increase or decrease in the natural frequency. As a result, the peak frequencies and their peak values in the frequency response function change.
The pressure change leak test detects a leak from the pressure drop observed after the container under test is filled with compressed gas and then closed. This method has the serious disadvantage of being sensitive to the temperature variation in the target container. We propose a new method using exponential analysis to compensate for exponential temperature variation in pressure change leak detection. In the proposed method, two successive leak tests are performed at different initial compression pressure. Exponential parameters of the temperature variation in the gas within the container are determined from the pressure signal in the first test, and the pressure in the second test is predicted using these parameters. The leak in the container is estimated from the difference between the predicted pressure and the measured one. Experimental results using a prototype leak detector and model piping showed that leak can be successfully detected without being affected by the given exponential temperature variation. With the proposed method, it was able to shorten the total test time by as much as 65% in comparison with the case in which a conventional leak test is performed after waiting until the exponential temperature variation settles. An algorithm using Discrete Fourier Transform for estimating exponential parameters from finite length data of pressure signal is also presented.
This paper presents a method for detecting and cancelling motion artifact related to standing and walking in a functional near-infrared spectroscopy (fNIRS) signal. Our fNIRS device has 22 channels. The motionless fNIRS signal from each channel is represented by a fourth-order autoregressive model (AR model), and the related parameters are estimated based on the motionless fNIRS signal using Yule Walker equation. The motion artifacts included in the fNIRS signal are cancelled using the Kalman filter constructed from the AR model. However, the cancellation may be insufficient when the motion artifacts are strong. To determine in which fNIRS channels the motion artifacts are cancelled insufficiently, we apply an observation prediction error related to the Kalman filter and a discrete Fourier transform. The brain activity of the user is then recognized from those fNIRS channels in which the motion artifacts are cancelled sufficiently. To evaluate the proposed method, a mobile robot is controlled using an fNIRS devise as worn by 10 subjects while standing, walking, or sitting. The success rate of brain-activity recognition by the proposed method was 64.2%, whereas that without the proposed method was 54.0%.
There is a growing need for molding process simulation of fiber reinforced plastics (FRP) in determining an appropriate set of process parameters, because a large number of process parameters exist and moreover those parameters have uncertainty or variability. Stochastic process simulations have been studied so far such as the Monte Carlo simulation (MCS), which provides us the expected value and standard deviation of the quantity of interest (QoI), considering the variability of input parameters. However, the results in the tail distribution were not highlighted except the authors' previous reports. This paper proposes a modified sampling scheme named stepwise limited sampling (SLS) to generate sampling points more efficiently and accurately in the multi-dimensional input parameter space, which lead to the tail distribution of QoI. The proposed method was applied to a resin transfer molding (RTM) process simulation considering 31 random parameters. Compared to the conventional MCS using 10,000 sampling points, it was demonstrated that enough number of cases in the tail distribution was analyzed by the modified method using only 1,700 sampling points.
As accuracy of industrial product was reduced by thermal deformation of a machine tool, a tool and a workpiece during cutting, there are several countermeasures for machining field. In the old days, we had developed and evaluated for a lathe with insensibility function for thermal and temperature change. The lathe has the structure of zero-center on three directions, the structure of self-compulsory cooling and the structure of thermal synchronism. Particularly the structure of thermal synchronism was developed for wet cutting. However the control method for the structure of thermal synchronism was yet to establish. Therefore the control using thermal synchronism at wet cutting in machine tool was developed and evaluated. The control system of fluid quantity on the structure of thermal synchronism using inverse analysis of neural network was developed for insensibility function of thermal and temperature change. Then thermal deformations of the developed lathe were measured and evaluated in the several experiments. It is concluded from the results that; (1) Thermal deformation of the bench lathe was very small in spite of no-forced cooling, (2) The control system of fluid quantity on the thermal synchronism using inverse analysis of neural network was effective for its working stability during wet cutting.
A linear machining technique using a nanosecond pulsed laser, adaptable for forming a single-point cutting tool made of nano-polycrystalline diamond, was developed. A basic study to find the principal rules of linear machining was conducted by forming an inclined face against the beam axis that is coincided with the Z axis. The face was formed by conducting repeatedly a set of machining processes, comprising linear machining to remove chips and zero-cut machining to remove the residual stock. It was verified through a machining test that the removal depth in the Z direction was independent of the inclined angle of the face. In addition, the stock removal in the Z direction coincided with the sum of the applied depths of cut in the Z direction when the residual stock removal in each machining step was eliminated by the zero-cut machining. These basic rules made it possible to accurately fabricate a convex dimple with a diameter of 0.2 mm, during which the inclined angle of the machined face against the beam axis varied at every position, by repeatedly conducting the set of machining processes. Also, it was verified through the forming test of a single-point cutting tool with a nose radius of 0.4 mm that the linear machining technique enabled the fabrication of the tool with a shape accuracy better than 1 μm and a cutting edge radius of less than 250 nm.
This paper proposes a scheme for imposing geometrical constraints in topology optimization for molding and milling so that optimal configurations that guarantee manufacturability can be obtained, based on the fictitious physical model. First, a level set-based topology optimization method is briefly described, and geometrical requirements for molding and milling are clarified. In molding, molded products must embody certain geometrical features so that mold parts can be separated, and milling cannot proceed unless the desired shape allows tool cutting faces to reach the workpiece. A fictitious physical model described by a steady-state advection-diffusion equation is then constructed based on the requirements. In the fictitious physical model, material domains are represented as virtual heat sources and an advection direction is aligned with a prescribed direction, along which mold parts are moved, or attitude in the case of a milling tool. Void regions, where the value of the fictitious physical field is high, represent either undercut geometries which would prevent the mold from being parted, interior voids that cannot be manufactured, or regions that a milling tool cannot reach. Next, a geometrical constraint is formulated based on the fictitious physical model. An optimization algorithm is then constructed. Finally, in the numerical examples, the proposed method yields manufacturable optimal configurations, confirming the validity and the utility of the proposed method.
To make sustainable society come true, product design is required to consider environmental issues such as reduction of resource usage, product disposal, and environmental loads. Many approaches for resolving these issues such as reuse, remanufacturing, and upgradable designs are studied and implemented. To apply these design approaches to product appropriately, a designer has to understand their characteristics and evaluate the product's adaptability for these design options. Hence, this paper evaluates the advantage of these design approaches. The ultimate purpose of this study is proposal of an adaptability evaluation method of product reusability, remanufacturability, and upgradability to support designer's decision making of product or component life cycle options at the early phase of design process. Thus, this paper speculates the appropriate perspectives of these evaluations and proposes conceptual evaluation method based on the viewpoints of society (low environmental load emission), manufacturer (low production cost and high profit), and consumer (low life cycle cost and high performance). Proposed evaluation method evaluates laptop's adaptabilities of aforementioned life cycle options quantitatively and shows that upgrading can satisfy the intents of environmental load emission, production cost, and life cycle cost. In addition, the agendas of this study are emerged. Particularly, evaluation perspectives with respect to product disassemblability, reliability, and pleasurability should be added. Additionally, improving evaluation method that can evaluate multiple perspectives comprehensively is also this study's agenda.
Error factors in sensorless cutting force estimation under ball-screw-driven stage were discussed. In addition, their influence on estimation accuracy was experimentally evaluated through several end milling tests. Because rigid body-based formulation is difficult in ball-screw-driven stage, estimation principle of cutting force needs to be formulated considering interaction between rotation and translation to enhance estimation accuracy of the cutting force. Simulation results revealed that phase lag element between current and position/angle response was non-negligible in higher frequencies as well as measurement error of acceleration due to numerical differential. Therefore, both phase lag compensation and high-resolution encoders are necessary. Fluctuations of disturbance force and acceleration synchronizing rotation of servomotor were classified in terms of their period: comparatively low-frequency fluctuations ranging from submillimeter to millimeter resulting from mechanical elements; high-frequency fluctuations with period of several micrometers resulting from interpolation error of encoder signal. The former can be eliminated more effectively than the latter, because preliminary identification is possible based on position dependency and repeatability. On the other hand, the latter needs to be eliminated by signal processing, because preliminary identification including phase is difficult. The result of milling tests revealed that it was possible to enhance estimation accuracy of the cutting force by constructing estimation system considering the above error factors.
In this study, we propose a parameter-free optimization method of material orientation for a shell structure consisting of orthotropic materials. We consider the compliance as an objective function and minimize it under the state equation constraint. The material orientation distribution is the design variables to be determined. This optimum design problem is formulated as a distributed-parameter optimization problem, and the sensitivity function with respect to the orientation variation is theoretically derived based on the variational method. The optimum orientation variations are determined by the H1 gradient method with the Poisson's equation, where the sensitivity function is applied as the internal heat generation on the shell surface, a driving force to vary the orientation in order to reduce the objective function while maintaining the smooth material orientation distribution. The optimum and continuously distributed orientation variations are determined as the temperature distribution of this fictitious heat transfer analysis without design parameterization. The optimum design examples show that the optimum the material orientation for the minimum compliance can be effectively obtained with the proposed optimization method.
Acquiring one's own form is an important technique for excelling in any competitive sport. Most basketball players spend a significant amount of time in acquiring the ideal form in order to improve their basketball skills. Although basketball is one of the most popular sports in the world, there are only few devices that aid in improving a player's skills. In the research involving the development of a skill-support device for basketball, it is important to learn the ideal form to acquire a physical posture of set-form. Therefore, we developed a device for reforming the set-form using auditory biofeedback. The proposed device measures the shoulder angle of a player in real time (50 Hz) and generates a sound on the basis of the measured angle to inform the ideal posture. If the set-form posture is not ideal, the device uses this sound to inform the player that they must modify their posture. The player then changes their shoulder angle and if the posture becomes ideal, the device mutes the sound. Several seconds after the sound stops, the device indicates the player to shoot. According to our study for testing the efficacy of this device, the BF-training group obtained 20% higher success rate than the control group. Moreover, the BF-training group had a more stable form than the control one.
Hardness identification is one of the most important tactile senses in humans. People use their hands in various ways to identify the hardness of an object. For example, acupuncturists identify stiffness in a muscle by pressing down with their forefinger held flat over the affected area. However, experimental evidence for the role of the pressing method in the identification of an object's hardness even when the same finger is used has not been shown yet. In this fundamental study, we investigated the differential threshold of hardness for different finger postures of pressing (pressing down with one's forefinger held “flat” or “vertically”) to determine the relationship between the different finger postures of pressing and hardness identification. We used seven elastic test pieces, each with a different Young's modulus, as the presented stimuli. We conducted an experiment using the constant method to calculate the differential threshold of hardness as a measure of hardness identification. The results showed that the differential threshold of hardness was higher when pressing down with a forefinger held “flat” than when pressing down “vertically” with the same force. This finding will be useful in evaluating the tactile identification of hardness in acupuncturists.
In this paper, we propose a system to identify the intention of motion based on the change of the surface shape of the upper arm. The proposed system uses six photoreflectors to measure the change of the surface shape of the forearm close to elbow joint. The changes of the surface shape of the forearm close to elbow joint are caused by muscle contraction. For this reason, the proposed system aims to be mounted on prosthetic hands for upper limb amputees who have residual muscular. Conventional identification methods of the intention of motion using photoreflectors were performed with a single motion such as grasping / releasing. In contrast, the proposed system identifies the six types of composite motions of hand and forearm. Complex processing is required to identify the six types of composite motions at a time. In the proposed system, it is possible to identify the composite motion by relatively simple multiple regression model, by separating into the motion of the forearm and the hand. In order to confirm the effectiveness of the proposed system, we conducted a discrimination experiment of composite motion by six volunteers and a discrimination experiment of composite motion at long-time use by one volunteer. As a result of the experiment by six volunteers, the average discrimination rate was 94.9 %. Moreover, the average discrimination rate of long-time use was 97.8 %. From these experimental results, we showed the possibility of discrimination of composite motion using photoreflectors.
A method has been developed for predicting the aerodynamic noise from the bogie of a high-speed train using a two-dimensional microphone array in a low-noise wind tunnel. First, the mean velocity distribution of flow was simulated precisely in the low-noise wind tunnel. Next, aerodynamic noise generated by the bogie, hereinafter referred to as aerodynamic bogie noise, was estimated from the noise source distribution measured with the two-dimensional microphone array. Finally, based on the experimental results, the predicted noise generated from the lower part of the car (i.e. the total of the aerodynamic noise estimated through the proposed method and the rolling and machinery noise estimated in a previous study) was compared with the measurement data obtained near the track in the field test. It was found that the predicted sound pressure level showed good agreement with those measured in the field test. This suggests that the proposed method is appropriate to estimate the aerodynamic bogie noise quantitatively. It was also shown that the contribution of the aerodynamic bogie noise to the total noise generated from the lower part of the car is greater than that of rolling and machinery noise, especially below 500 Hz.
The escalator is one of most important vertical transportation measures to connect each every one of storey-layers in buildings. During severe earthquakes, escalators are not only shaken by themselves, but withstand lateral relative deflexions induced in the structures or buildings installing them. Therefore, escalators are usually installed in the buildings with one side of them in fixed connection and the other side in free condition or utilized both sides in the non-fixed style in order to mitigate undesirable excessive deflexions induced in the truss-like structures of escalators. However, in the 2011 Pacific Ocean Tohoku-Oki Earthquake, fall accidents of four escalators occurred in the three locations. Escalator truss might come off from the beam of the building, because excessive lateral deformations were induced in the storey-layers with more than assumption where the accidents happened. During these accidents, it was also considered that a non-fixed part might collide with the beam of building by larger deflexions than expected occurred in the sliding parts; this collision might cause excessive compressive force and residual displacement in the escalator truss might be caused (Miyata et al.). Projects for the building standard development promotion program have been conducted by Japanese ministry of land, infrastructure and transport (MILIT) in order to improve and maintain the building standard by applying non-government organizations such as research institutes, private enterprises and universities. In these projects, investigations regarding elevators and escalators have been implemented since 2010. Especially in 2014, the loading tests were carried out to clarify the behaviour in such excessive condition using eight full size escalator-truss model at the Chiba NT campus testing cite of Tokyo Denki University. The results obtained in the tests have already been applied to the building standards law revision and the notice amendment (Tokyo Denki University and MILIT). From the above-mentioned background, the object of this research is to construct an analytical model to clarify the seismic response behaviour using the non-linear restoring force characteristics of the escalator truss model. In this first step of the study, an analytical model using a single degree of freedom model considering not only the non-linear behaviour of escalator truss but also the sliding friction occurring between the beams of buildings and escalators has been developed.
It is important for railway bogies to get compatibility between curving performance and running stability. Utilizing independently rotating wheels may be an effective solution. The EEF bogie proposed by Dr.Frederich in late 1980th shows good curving performance making use of the gravity restoring force generated by the tread gradient of independently rotating wheels. However, the bogie gives rise to a kind of hunting motion as the vehicle running velocity increases. In this paper, an effective modification of the EEF bogie which solves the hunting motion is mentioned. The solution is to incline both wheel-axles while adjusting the tread shape of each wheel. In this paper, the EEF bogie with inclined wheel-axles is firstly proposed and analytically evaluated by the MBD simulation. Since the newly proposed bogie has complicated structures, a precise modeling of the bogie is mentioned in detail. From the result of eigenvalue analysis, proposed bogie can dramatically improve the hunting stability as compared to the conventional EEF bogie. In addition, the proposed bogie has excellent curving performance in tight curve section equivalent to the conventional EEF bogie. As those results, it is possible to achieve both high speed hunting stability and curving performance utilizing the proposed bogie unit in the vehicle.