A strain measurement system based on astable multivibrator using CMOS inverter has been developed. This system could omit an amplifier, filter and A/D converter unlike conventional Wheatstone bridge type sensor, because strain is measured by counting frequency of circuit voltage output due to resistance changes of a strain gauge. In the previous studies, it was shown that static strain could be measured with the same level of accuracy as Wheatstone bridge circuit. However, it was found that the sampling frequency for counting was not high (around 1 Hz) and it was difficult to measure dynamic strain. A reciprocal counting method has been applied to the system to improve sampling frequency in this study. Fatigue tests of a notched specimen were carried out and strain was measured during the tests to compare performance between the developed sensor and original sensor. As a result, strain could be measured with high frequency by the developed sensor. It is also found that strain measurements with high frequency could detect crack propagation state during the fatigue tests.
In this study, the natural frequency of cylindrical sandwich tube with lattice core has been investigated using finite element method (FEM). In particular, effects of geometrical parameters such as the ratio of the diameter to length, unit-cell size and facesheet thickness on the natural frequency were discussed. It is revealed that the natural vibration frequency of the lattice sandwich tube can be predicted with a good accuracy in a wide range of tube length-to-diameter ratio L/D by substituting the equivalent material properties (initial stiffness Eeq and Poisson’s ratio νeq) and relative density ρeq into the analytical equations for a straight tube of a continuum medium.
Sound generated aerodynamically from a flow around an airfoil subjected to inflow turbulence is investigated experimentally as well as numerically to identify the dominant source of the sound. The test airfoil has NACA0012 wing section with a chord length of 150 mm and a spanwise length of 500 mm. The wind speed is set to 30 m/s, which results in an airfoil Reynolds number of 3.0×105. Wind tunnel experiments are conducted with Active Turbulence Generator (ATG) set at the nozzle exit to control the turbulence intensity and the eddy scale of the inflow turbulence, independently. The former is varied from 10 % to 20 % while the latter is varied from 300 mm to 1600 mm. Large eddy simulation (LES) with turbulent grids is also performed to investigate the flow field around the airfoil in further detail, for which the turbulence intensity is 10 % and the eddy scale is 3.75 mm. As a result, we have found that the pressure fluctuation near the leading edge of the airfoil is remarkably high, and therefore, it is most likely the cause of the considerable increase in the sound generated from the airfoil. In addition, the correlation between the airfoil lift force and the angle of attack for the airfoil subjected to the inflow turbulence is not very high, and therefore, the change in the lift force due to the change in the angle of attack is least likely to the cause of increase in the sound.
The effect of apex and attack angles to the flow around a pyramid obstacle was investigated with flow visualization and laser Doppler velocimetry. The flow visualization was performed by dye injection and electrolytic etching methods. The Reynolds number based on the height of the pyramid is 600. The apex angle, 2α, is in the range of 15 through135 degrees, and the attack angle,γ, is 0 and 45 degrees. It seems like the flow in upstream region of the pyramid is divided into two patterns; two and four vortex systems. The height of the primary vortex of horseshoe vortices takes a maximum value around 2α=90 degree for γ=0 degree, but 2α=45 degree for γ=45 degree. The height for γ=45 degree is lower compared with the result for γ=0 degree. The dependency on 2α and γ of the additional stain rate due to the obstacle can be formulated with the spanwise component of fluid velocity along the obstacle surfaces and the streamwise projected base width. The maximum vorticity, |Ω|maxδ*us /U∞ where U∞ is free stream velocity and δ*us is the displacement thickness near the upstream separation point, of the primary vortex varies depending on the magnitude of the vortex stretching due to the additional strain rate multiplied by time scale that the fluid passes through the obstacle. The vortex system is two vortices for |Ω|maxδ*us /U∞ <1.5, and four vortices for |Ω|maxδ*us /U∞ >1.5.
Measurements are made by a newly designed high-precision thermo-anemometer in the wake of a heated cylinder of D=0.013 and 0.030 m. The purpose of this work is to make clear the effects of cylinder heating on the mean field in the wake. Temperature and velocity distributions are obtained for X/D=5 - 40. Reynolds numbers for unheated case are ReD=3000 - 10000 and temperature difference between the cylinder surface and the ambient air reaches Δθ=0 - 225 ℃. The effects of cylinder heating on the mean field are as follows : Normalized maximum values of θmean/θr , θrms/θr, urms/U0 and vrms/U0 in each Δθ and U0 have similar logarithmic decay tendencies occurred by vortex breakdown. When Δθ is same, the mean gradient of each parameter distribution becomes smaller with ReD decreasing because of Richardson number RiD increasing. Values of urms/U0 and vrms/U0 are increased, wake structure is made asymmetrical, and vortex collapsing is accelerated by cylinder heating.
This paper shows a singular mechanism for a gravity compensated and reactionless robot arm. Firstly, the difference between singular point and singular mechanism is explained. A Simple example shows that singular point is local but singular mechanism is global. In other words the latter singularity is globally maintained. Secondly, four characteristics are introduced. The first one is gravity equilibrium, the second is centroid immobility, the third is conservation of angular momentum and the last is constant posture. Gravity compensation is made possible by gravity equilibrium, and no reaction is made possible by centroid immobility and conservation of angular momentum. Thirdly, a robot arm using a singular mechanism is introduced, and characteristics of no reaction are shown by a computer simulation. Finally, it shows the motion range of the arm as an issue.
A design method of a strongly coupled vibration system is required for improving noise and vibration performance of machinery. One of the authors proposed that analysis of the self-compliance matrix at interface degrees of freedom between two systems, called as kernel compliance matrix, gives the insight to work out satisfactory countermeasures for resonance frequency control of a strongly coupled vibration system. The approach, however, is only feasible for a two by two kernel compliance matrix. To expand this approach to an N by Nkernel compliance matrix, a coordinate transform is available to reduce the matrix dimensions. However, the selection of the basis vector is not so easy. This paper presents a practical approach for the analysis of an N by Nkernel compliance matrix. In this paper, it is shown that structural modification for resonance control can be derived using the Wedderburn’s rank-one perturbation of a kernel compliance matrix. Finally, this approach was verified by a numerical case study.
The author proposed the identification method of symmetric nonlinear system based on the Auto-Regressive analysis and the method of averaging in a previous paper. However, there is a problem that conventional methods including the one in the previous paper cannot address the identification of asymmetric vibrating systems. In this paper, the system identification in asymmetric nonlinear system is investigated. At first, formulation of identification problem is conducted. The identification problem is described using the method of Krilov-Bogoliubov-Metropolsky is considered the two-order approximation. The description contains the amplitude dependency however coefficient of the sign cannot discriminate. Therefore, this paper proposes a new system identification method to solve these problems by identifying appropriate sign of nonlinear parameters based on movement of center-of-vibration. Identification experiment is conducted using numerical investigation, Runge-Kutta method. A nonlinear coefficient is considered in two cases: positive number and negative number. In both cases, the proposed method gives good estimated results which show good agreement with the true values. Moreover, identification experiment is conducted using the cantilever system subjected to the magnetic force. The proposed method gives estimated results which shows good agreement with the true experiment values.
A working six-legged robot which can switch three modes of locomotion and manipulation by using some legs as arms is under development: six-leg mode and two kinds of four-leg two-arm modes, where the robot holds and manipulates an object with two arms. Attaching hands to the legs enables five-leg one-arm mode; the robot grasps a small object with one hand and manipulates the object with one arm, while walking stably with five legs. Because the arm has three DOF, the robot needs to move its body with the five legs in order to control the pose of the hand. The present paper proposes a coordinated control method of five legs and one arm to manipulate five-DOF pose of the hand. The robot stands on the five legs. From the desired velocity and angular velocity of the hand, the joint velocities of the arm and the velocity and angular velocity of the body are determined. From the determined body velocity and angular velocity, the joint velocities of the five legs are obtained. These joint velocities are commanded to the robot. If at least one of the five support legs reaches the limit of its movable area, the robot stops the arm and body temporarily. Then the five legs step to the center of their movable areas. After the five legs finish stepping, the robot resumes the control of the hand. Experiments of moving the hand along straight lines show the validity of the proposed method.
In this paper, a numerical integration method for real-time vehicle dynamics analysis with multibody technique is discussed. When the effect of the deformation of a rubber bush is considered in a multibody simulation, the rubber bush is usually defined as a force element with a high-stiffness property. In this case, the multibody vehicle model contains high frequency modes. As a result, the multibody vehicle model requires a small step size for the numerical integration. In this research, the real-time simulation with a multibody vehicle model was realized by the generalized-α scheme, which allows a dissipation of high-frequency modes with keeping the accuracy in low-frequency modes. In order to evaluate the influence of the parameter for the generalized-α scheme on the accuracy of an analysis result, the authors propose to derive a transition matrix from numerical simulation results. In addition, a methodology of choosing the parameter for a real-time simulation is also mentioned. It was confirmed that a stable real-time simulation with multibody vehicle model including the rubber bush properties can be performed with keeping high accuracy for low frequency modes by choosing a proper parameter according to the methodology.
Cymbals are percussion instruments that vibrate and radiate sounds when hit with a stick. A bell is the raised section in the middle of the cymbal and its size produces different sounds. In this study, we investigate the effect of bell size on the sound characteristics of cymbals. The radiated sounds and vibrations for cymbals with two different bell sizes are measured. In addition, the natural frequency and mode shape are obtained by finite element analysis and the sound radiation efficiency is calculated for each mode. The measured results indicate that the sound frequency characteristics for the large bell show three peaks with large sound pressure within the range of 1000 to 3000 Hz and the sound pressure for the small bell is larger than that for the large bell within the range of 4000 to 5000 Hz. The vibration frequency characteristics show there is no remarkable difference between the large and small bells. The sound radiation efficiencies indicate that the large bell has many modes with high radiation efficiency within the range of 1000 to 3000 Hz and their modes have a small number of nodal diameters and a large deformation at the bell. The small bell has many modes with high efficiency within the range of 4000 to 5000 Hz. This is reason for the difference in sound characteristics between the large and small bells.
The railway current collection system consists of a line and a pantograph. We take up the problem of the contact loss between a rigid conductor line and a pantograph. In order to avoid the damage on the line surface by the electric ark, it is important to prevent the contact loss. From the series of experiments with an actual pantograph system, an essential model that regards the contact loss as impact oscillations between a rigid conductor line and a pantograph was proposed. This model consists of a spring supported mass and an external exciting source that is pushed against the mass. In this paper, in order to suppress the impact oscillations, we add an oscillatory system coupled to the spring-mass system. Then, we consider the impact oscillations between the excitation source and the main mass in the two-degrees-of-freedom system. We numerically investigate the problems and obtain the bifurcating motions. When the exciting frequency is near the second mode natural frequency in the two-degrees-of-freedom system, the impact oscillations between the main mass and the external excitation source is suppressed. We conducted a series of experiments in order to verify the theoretical results. The experimental results also reveal the suppression of the impact oscillations. The experimental results qualitatively well agreed with the theoretical predictions.
In Japan, the number of people who have difficulty walking has been increasing with the rise in the aging population and that of people with physical disabilities. Individuals with athetosis-type cerebral palsy must use electric wheelchairs due to abnormal walking. However, since they have problems with fine motor control, including the occurrence of involuntary movements and difficulty maintaining posture, they have difficulty intentionally controlling their hand movements. Therefore, they cannot operate a joystick, even if they desire to use electric wheelchairs, and there are risks of accidents. In this study, by considering the arch structure of hand, we developed a new joystick grip that enables the suppression of involuntary movement. We evaluated our proposed grip by comparing running stability with a conventional grip, and demonstrated the effectiveness of proposed method.
A numerical calculation scheme for stress and its consistent tangent moduli with hyper-dual numbers(HDN) for Ogden-type hyperelastic material model was proposed. The main advantage of this scheme is that once the framework is coded, any Ogden-type hyperelastic material model can be implemented by only re-coding the strain energy density function. In this scheme, the new differentiation method for eigenvalue and eigenvector of the symmetric matrices with HDN were proposed. The proposed method can calculate the eigenvalue and eigenvector in non-real part analytically by using the eigenvalue and eigenvector in real part, in case that all eigenvalues in real part are not multiple root. We implemented the Neo-Hookean model and the Ogden model with the proposed scheme, to confirm the effectiveness and robustness of this method, and applied it to some examples. As the results, it was confirmed that the numerical results of the proposed method showed good agreement with analytical ones.
Mounted on high pressure washers, reciprocating pumps use oil for lubrication and cooling. If the lubricating performance is insufficient, problems such as a decrease in efficiency, seizure, and adhesion occur. Therefore, ensuring optimal lubrication performance is necessary. However, calculating the oil churning behavior due to the complex nature of dynamic oil flow within the crankcase is difficult. If the oil churning behavior can be calculated qualitatively and quantitatively via simulation, design study will be simplified and development costs could be significantly reduced. Considering these conditions, herein, we quantified the oil churning behavior within the crankcase using the MPS (Moving Particle Semi-implicit) method and thus improved the lubrication performance of the pumps. In the new design, the crankcase has an elliptical shape with ribs on the inside. We expect to have sufficient lubrication performance with less oil, because the churned-up oil is efficiently guided to the rotating part by the rib effect. The validation was evaluated by an operation test using a prototype. As a result, it was confirmed that the oil stayed clean in the new design.
This paper describes basic study of sheet attitude during accelerated delivery of the nip transport mechanism. The nip transport mechanism with a pair of rollers is widely used in many devices, such as automated teller machines (ATMs), printing machines, etc. In these machines, a sheet is sometimes nipped by two pairs of rollers rotating unequal speed. There are two kinds of the conveyance between rollers with unequal speed, namely, accelerated delivery and decelerated delivery. The sheet attitude during the accelerated delivery and the decelerated delivery can be changed. In this paper, we presumed the parameters that affect the sheet attitude during accelerated delivery. Furthermore, we clarified the influence by observing the sheet attitude in actual transport. As a result, we have found a method to stabilize the sheet attitude during accelerated delivery.
Recently, crowdsourced manufacturing concept highly attracts attention. In crowdsourced manufacturing, each participant shares its manufacturing resources to improve asset efficiency. To realize this concept, it is important how to make matching between resource requests and resource offers which achieve high efficiency improvement in fair way. Previously, some authors showed production efficiency improvement with some resource matching algorithms. But, accumulation of knowledge about the design of crowdsourced manufacturing is not sufficient currently. To support the design of crowdsourced manufacturing system, we previously proposed an evaluation method based on matching stability analysis for resource matching between resource requests and offers. The previous computational results showed that the system profit maximization policy made resource matching plans instable. In this research, we propose a balancing method between the system profit and the matching stability based on the 'nucleolus' concept in cooperative game theory. The proposed method reduces the maximum dissatisfaction of each resource request with procurement cost sharing. The computational experiments show that the proposed method improves resource matching stability with keeping system profit level in most cases. It cannot be generally stated how much the dissatisfaction with the resource request can be regarded as a virtually stable matching. So, it is important to evaluate property of crowdsourced manufacturing system with computational simulations and discuss politely among the participants before decision of the design of crowdsourced manufacturing system. In the future, we will examine resource matching methods from the viewpoint of the strategyproofness concept in market design theory, and evaluate them in various scenarios and in real manufacturing environment to clarify which situation is appropriate for crowdsourced manufacturing.
Built-up Layer (BUL), produced by accumulating workpiece on the tool rake face, has the tool protective effect and the smaller depth of overcutting during cutting of metal material. The main objective of this paper is to clarify the influences of coating characteristics on the BUL formation process during cutting of titanium alloy. Dry cuttings of Ti-6Al-4V with three different cutting tools (uncoated, PVD coated, and CVD coated carbide tools) were conducted. After the cutting tests, the cutting tools were observed through laser confocal microscopes (LCM) and scanning electron microscopy (SEM). The BUL formation conditions were examined from the viewpoint of the adhesion’s shape, surface roughness, and the amplitude variation of cutting force. From the results, as expected, it was confirmed that BUL can form on the tool rake face for different tools at the cutting speed below 50~70 m/min and it can protect the tool rake face from wear to some extent. It was also determined that the coating characteristic nearly has few effects on the BUL formation mechanism but it can change the size of BUL and affect the stability of BUL. On the other hand, the BUL formation played a great role on the fall-off of coating. Finally, the ability of BUL to decrease the tool wear was also analyzed. The results indicated that BUL can be used to decrease the tool wear formation and to extend the tool life at the cutting speed below 70 m/min during dry cutting of Ti-6Al-4V and the size of BUL plays a decisive role in the protective effect.
We developed a brake shoe made of a fluorine-contained rubber (FKM) compound filled with rice bran ceramics (RBC) particles for a caliper brake of bicycle and evaluated the braking performance and tribological properties on the wet condition from high running speed to stopping. In addition, we investigated the influence of the RBC particles on the braking performance and tribological properties. The test apparatus consisted of an actual bicycle and imitated a rainy condition. The brake wire pull force was 60 N, which corresponded to a low grip force. We manufactured FKM shoe and RBC-contained FKM rubber (FKM/RBC) shoe as the test samples. A well-regarded commercially available rubber shoe, which included hard inorganic fillers, was compared with the other test samples. The FKM and commercialized shoe samples exhibited the high friction coefficients in the initial stage of test cycle whereas the coefficient of the commercialized shoe rapidly decreased with the test cycles. The FKM/RBC shoe sample had the stable and high friction coefficients irrespective of test cycle. The specific wear rate of the FKM/RBC shoe was much smaller than the other samples. Furthermore, the aggressiveness to the rim was lower for the FKM/RBC shoe than that for the commercialized shoe. We concluded that the RBC filler possessed the characteristics to maintain the braking performance irrespective of duration of use and to reduce the wear of the shoe and rim under rainy conditions.
The aim of this study was to investigate the effective parameters of eye movement for estimation of mental workload (MWL) during automobile driving by using a visible light camera. Twelve students (6 males and 6 females) participated in this study. The participants performed a driving task with a driving simulator and a secondary task simultaneously. The N-back task was taken as the secondary task so as to control the MWL. The levels of N-back task were as follows: none, 0-back, 1-back, 2-back, and 3-back. The gaze and head angles and blink frequency were measured with a visible light camera. The eyeball rotation angle was calculated from the gaze and head angle. The sharing rate of head movement, which is the ratio of head movement against the gaze movement, was calculated. The subjective MWL and accuracy of N-back task were also measured. The result showed that the subjective MWL monotonically increased with the increase of the difficulty of N-back task. The effect of the difficulty of N-back task was statistically significant for the standard deviations (SDs) of horizontal and vertical gaze angle, SD of horizontal eyeball rotation angle, sharing rate of head movement in horizontal direction, and blink frequency. The result of logistic regression analysis showed that the SD of horizontal eyeball rotation angle and blink frequency were the most significant parameters to estimate the MWL. The area under the curve (AUC) of receiver operating characteristic (ROC) curve for the regression equation was 0.822; thus, it has relatively high discrimination ability on the MWL.
Advanced light distribution control technology of the headlamp has developed and it is becoming possible to present information to the driver by graphics on the road surface as well as forward irradiation by ADB. On the other hand, the effect of presenting risk information by the function of the advanced headlamp on driver’s behavior is not clear. In this study, we set various irradiation patterns of headlamp on the driving simulator and conducted experiments on collision avoidance behaviors at night. As a result, it was confirmed that the brake reaction time of drivers presented risk information by the headlamp to the road surface was shorter than drivers without presenting information. Also, we found that drivers perform brake operation more strongly by presenting rectangle-line based on the stopping distance algorithm on the road surface. Presentation of rectangle-line indicating the braking distance seems to reduce the frame line from the front of drivers, it was confirmed that this presentation method was easily recognized as a warning by drivers. Furthermore, the probability of collision against the obstruct was determined by data simulation based on the driving operation data obtained in the experiment, and it was found that the probability of collision decreases due to the risk information presentation.
The crash safety structure of the railway vehicles is effective as one of the safety measures against the train crews and the passengers in the event of a collision accident. The standards for crashworthiness of railway vehicles are defined in Europe and the U.S., while there are no standards for crash safety in Japan. Therefore, it is important to establish the evaluation method for crashworthiness of railway vehicles considering the actual situation of collision accidents in Japan. The authors carried out finite element analyses of a level crossing accident under various conditions (collision speed, mass of the obstacle and relative position between the train and the obstacle) based on the statistical analysis of serious level-crossing accidents in the past in Japan, and calculated the deceleration time histories in the passenger area under each condition. We evaluated these deceleration waveforms according to European and the U.S. standards for crashworthiness, and we also performed finite element analyses of dummy’s behavior and injury values using these deceleration waveforms as input. We verified the correlation between the evaluation results in terms of the deceleration according to these standards and dummy’s injury values obtained by finite element analyses. As a result, the evaluation according to the velocity at which a passenger contacts the seat back ahead of him (the U.S. standards) was the most effective. Moreover, the integrated values of the deceleration of the passenger area during an integration time t360 had the highest correlation with the dummy’s injury values.
In our daily life, there are barriers such as a step, stairs and etc. It is difficult to get over such barriers by commercially available powered wheelchairs. From this reason, many people are developing a new personal mobility vehicle (PMV) that can climb a step. However, the safety during step-up-motions is not considered enough. One of the ideas of improving the safety during a step-up-motion is a right interruption of the motion. In this study, we consider resetting motions when a PMV climbs a step. RT-Mover (Rough Terrain Mover) PType 2, which can move on paved road and get over rough terrain including steps, is employed for experiments. We discuss the resetting motion according to the following procedure: firstly, possible motions for resetting the leg motion are picked up. Secondly, contents in the experiment are discussed. Finally, experiments are conducted for evaluations. Through the above, the most comfortable resetting motion is selected.
To shorten the stopping distance of the high-speed trains in case of emergency such as a huge earthquake, the author developed the small-size and light-weight aerodynamic braking device. The device increases an aerodynamic drag force of a train to achieve a high deceleration at the range of over 350 km/h without a friction between rail and wheel. The device is as miniaturized as possible in order to be installed flexibly on the train, whereby many devices with small-size drag panels are appropriately arranged throughout the train roof to obtain higher drag force. A pair of drag panels rotating around a horizontal axis which are connected by the gear can be actuated by the traveling wind without a large-size actuator. The full-scale prototype aerodynamic braking device is designed and manufactured. To examine its aerodynamic characteristics, one or two prototypes are tested on a wind tunnel facility at a maximum flow speed of 400 km/h (111 m/s). It was proven that the response time of motion from the folding position to the braking position took only 0.39 s, and the device could produce the aerodynamic drag of 2.3 kN per one unit at 400 km/h. Detached-eddy simulation (DES) is used to study the flow around a train roof with a large number of devices. The rate of change of the drag coefficient for devices with the staggered arrangement which aims to improve a total drag force of a train is compared against the standard parallel arrangement at U = 360 km/h. The staggered arrangement could increase the total drag coefficients 10.3 percent as compared to the standard parallel arrangement.
Among the demands for energy saving and high efficiency improvement of equipment, comfort is required as added value. Vibration and noise during elevator travel propagate into the car, which induces a feeling of ear blockage and car shaking. As a result, the ride comfort, which is one of the comforts, is reduced. In this paper we focus on the ride comfort of the elevator. In order to evaluate the ride comfort of the elevator, an elevator that can change the rated speed and control acceleration when going up and down is used. By using this elevator to acquire data, we combine human subjective evaluation and objective evaluation by physical quantity to extract parameters that affect ride comfort. As a method, each index is extracted by multivariate analysis of sensory evaluation data and physical evaluation data, and they are subjected to multiple regression analysis to make association. As a result, the parameter to be affected is acceleration, and in particular, it is effective to reduce the longitudinal acceleration of the human being for riding comfort. Therefore, it can be expected to devise a method to realize a comfortable ride comfort with an inexpensive system by limiting the countermeasure points of the elevator.