In recent production environment, many factories introduce mixed production system to simultaneously produce multi-types of products. Ordinarily, multiple work elements are assigned to workers or work centers in the process of process design to aim at high productivity. However, fluctuation of operation times is normally included in mixed production line and capacity of buffer affects productivity of the line. In this study, we deal with the problem of process design for mixed production line including fluctuation of operation time. In addition, we treat the problem of process line as multi-objective problem. In this paper, multi-objective genetic algorithm is developed to resolve the problem to minimize the bi-objective functions: the maximum value of operation time at all work centers and the maximum value of dispersion of operation time all work centers. Numerical experiments are performed to evaluate performance of the algorithm and characteristics of solutions. Productivity of the production line designed by the proposed algorithm is evaluated by using event-driven simulation. Simulation result shows that production line designed by the proposed mathematical model generates high productivity and small size of WIP when buffers are located between work centers.
The cell manufacturing system of a labor concentration type is still in the important position of the manufacturing industry at this stage. Since an operator's skill is greatly related to productivity in labor concentration type cell productions, the operator's effective training is important. On the other hand, when operators learn and acquire the multi-skill tasks, the level of difficulty in their mastery depends on the contents of target operations, so a sufficient plan for training is required. In this study, the main objective is the rapid improvement of operator's skill. Therefore, after classifying operator's skills about all the operation tasks, we try to optimize the task allocation in training mode, and evaluate its validity quantitatively.
In recent years, manufacturing industries are required to provide various kinds of products in a short time. They are also required to reduce the effects on the environment. In sheet metal processing, to achieve these requirements, process planning and production planning should be managed suitably. For process planning, nesting is done in order to design the optimal layout for sheet metal in terms of reduction of waste material. Scheduling is done in order to satisfy the due date of products. Nesting and scheduling are affected with each other and there occurs a certain trade-off between them. Therefore, those problems should be considered simultaneously in order to increase the efficiency of entire manufacturing activity. Under such understanding, we propose an integrated method of scheduling and nesting. In its procedure, scheduling is firstly executed by using dispatching rule. Then, based on the result of scheduling, nesting is executed by using bottom left algorithm. Moreover, to update the nesting result, the layout is redesigned by reallocating parts in each sheet metal according to its size. Finally, in order to validate the effectiveness of proposed method, we implemented prototype of nesting scheduling system and carried out computational experiments. The results are compared to a conventional method in terms of total tardiness and the number of sheet metal. To validate the effectiveness of reallocation, yield rate is also compared between the proposed method with and without reallocation.
Under growing concerns with sustainability in global and changing market, cooperative and competitive logistic is becoming a keen issue to provide a manufacturing system aligned to sales and operations planning (S&OP). As a key technology for such deployment, this paper concerns with simultaneous pickup and delivery VRP and proposes a hybrid method aiming at a rational decision aid for logistics optimization. In its procedure, the initial solution is derived from the Weber basis saving method that accounts transportation cost in terms of the bi-linear model of distance and weight. Then, to update the tentative solution in turn, a modified tabu search developed previously by us is used successfully. Though this practical cost accounting has been used popularly in the strategic location problems, it has never been applied to the operational problem like VRP. The idea is possible to extend naturally to a non-linear or generalized Weber model to be more practical. Since the developed method is practical and adaptive even to large problems, it has high solution ability available for real world applications. Finally, numerical experiments are taken place to validate the effectiveness of the proposed method through comparison with an alternative manner to accomplish the present task.
In this paper, authors introduce an AR application which supports a pipe drawing work in a shop floor of a shipyard. Some pieces of pipes are not designed beforehand in ship design process, as they contain uncertainty caused by pipe production and assembly in a factory. These pipes are usually designed and fabricated individually in a shop floor by the method that is far from be digitalized. The piping work of gauging pipes takes an immense amount of time. Because those works are composed of 3 processes, measurement of relative position of both ends of flanges, design of the pipe and confirmation of the piping design. In order to reduce the time of those piping work, the authors have developed the AR application which can design the gaging pipes automatically. The AR application measures the location of both ends of the pipe using image processing, automatically draws a suitable shape of the pipe, and effectively illustrates graphics of the pipe as AR once the worker holds a tablet PC to the direction he wants to fix the pipe. The paper explains details of above AR applications, including those system diagrams, and shows some results of demonstration for easy understanding how they work.
SMA (Shape Memory Alloy) is utilized in various fields. Especially, Ti-Ni alloy has excellent features than other SMA. And, the alloy has two kinds of the phase transformations of rhombohedral (R) and martensitic (M) phase. Though R-phase transformation is not suitable for large deformation, it has been reported that its function for the cyclic deformation is steady. However, the detailed regulation for evaluating the function deterioration and life of the transformations has not been determined, because each factor affects the complexity to each other. Therefore, the establishment of the technique which evaluates the deterioration by the cyclic deformation is desired. In this study, the features of the AE (Acoustic Emission) signals detected in tensile and cyclic deformation test and the structure analysis results of the simulation with MD (Molecular Dynamics) method were compared. As the results, the following things became clear. The frequency components of the signals detected by R- and M-phase were about 750 and 350 kHz respectively. The properties of the signals in each phase showed the chaoticity, and they changed with the increase in the stress. The occurrence behaviors and features of the signals changed with the transitions of the hysteresis loop of σ-ε diagram by cyclic deformation. The generation condition of the R-phase seldom changed in the deformation until rearrangement of R-phase. On the other hand, the conditions on R- and M-phase decreased in the cyclic deformation until M transformation, because the residual phases disturbed the occurrence of M-phase. By observing the simulation results, it was possible to show the existence of the phase transformations of "Austenite (A) phase→R-phase→M-phase" and "A-phase→M-phase". And the correlations between those generation behaviors and the characteristics changes of the signals were recognized.
Thermal barrier coatings (TBCs) have been deposited onto the blade surface in a land-based gas turbine according to increase of turbine inlet temperature (TIT). In service of those gas turbines, it has been known that cracking and delamination in TBC is one of the serious damages. Thus, it is very important issue to assure the reliability for TBCs or advanced protective coatings in service. The aim of this study is to clarify how micro damage progresses in TBC and porous TBC, which is called P-TBC here, under a tensile loading at a high-temperature environment. Here, P-TBC has been developed by Arai in order to reduce thermal conductivity and infiltrate coolant gas for achieving transpiration cooling technology. As a result, the surface cracks propagated in a direction perpendicular to the interface in both TBC and P-TBC samples. When a tip of those cracks reached the interface, the crack was curved along the interface between substrate and bond coat in case of TBC sample at room temperature especially. On the other hand, the surface crack propagated along the interface between top and bond coats in case of P-TBC sample. In the tensile test conducted at 1273K, the crack path was located at the interface between top and bond coats in both TBC and P-TBC samples. The quantitative evaluation revealed that critical strain up to crack initiation was almost the same at TBC and P-TBC, and number of cracks per length in TBC sample was higher than that of P-TBC. The J-integral-based adhesive strength of TBC sample was stronger than that of P-TBC.
Effect of humidity on the growth mechanism of a fatigue crack in an age-hardened Al alloy was investigated in relative humidity environments of 25% and 85% at loading frequencies of 50Hz and 6Hz. Macroscopic growth mode of a crack in low humidity was a tensile one irrespective of loading frequency. By contrast, the mode in high humidity was changed from the shear one to the tensile one with increase in fatigue life at 50 Hz, while it was the tensile mode only in the wide range of fatigue life at 6 Hz. In low humidity, the crack propagated by forming striations which are general in fatigue of many metals. On the other hand, in high humidity, most of fracture surface was occupied by many slip planes in the shear mode crack and by granular facets in addition to striations in the tensile mode one. The crack growth rate in high humidity was higher in the shear mode crack than in the tensile mode one. The differences in growth mechanism and growth rate of a crack were explained by the content of diffused hydrogen generated by reaction of water vapor and aluminum in addition to the microstructure with sub-grain and texture and the cyclic softening behavior of the alloy.
In fabricating complicated laminated composite structures by using prepregs, various kinds of fiber discontinuities such as ply drop-off and seams can be formed. Special care must be taken for the fiber discontinuity since they can induce stress concentration, and damage onset and growth originated from them may lead to catastrophic failure of the structure. The present study evaluates mechanical behaviour in unidirectional CFRP laminates that contain centered or dispersed fiber discontinuities fabricated by using interlaminar-toughened CFRP prepregs. Tensile testing has shown that higher onset stress of the interlaminar delamination between continuous and discontinuous plies can be achieved by interlaminar-toughened CFRP with centered fiber discontinuity compared to that for conventional CFRP prepregs. As for the specimen with dispersed fiber discontinuities, fracture stress keeps almost constant with more than 20 mm of interval of the dispersed fiber discontinuities. By applying the onset stress of the delamination that is experimentally obtained using centered discontinuity to an analytical model, critical energy release rate by the delamination onset is calculated. Then it is indicated that one can predict the fracture stress of the specimen with the dispersed fiber discontinuities with more than 20 mm interval of the discontinuities by using the critical energy release rate. This indicates that fracture of the laminate is dominated by the interlaminar delamination between discontinuous plies with more than 20 mm of interval.
Fatigue properties of shot-peened high strength Al-Cu-Mg alloys, extruded and drawn 2017-T4 alloys, and effect of humidity on the properties were investigated in relative humidity environments of 25% and 85% under rotating bending. Fatigue strength was increased by shot-peening in each humidity. Although fatigue strength was largely decreased by high humidity in the electro-polished specimen, the decrease in fatigue strength was very small in the shot-peened one. In the electro-polished extruded alloy, the crack propagation changed from a shear mode to a tensile one with decreasing in stress level in high humidity, while the propagation in the shot-peened one was in a tensile mode only in both humidity environments similar to the ones in both of the electro-polished and the shot-peened specimens in low humidity. The propagation mode in the drawn alloy was a tensile one irrespective of stress level and humidity. Most of fracture surface in low humidity was occupied by striations in both of the electro-polished and the shot-peened specimens in both alloys. On the other hand, those in high humidity were covered with slip planes in the shear mode crack in the electro-polished extruded alloy, while a few granular facets in the extruded alloy or brittle striations in the drawn one were observed at the fracture surface in high humidity in addition to striations in the tensile one irrespective of stress level and shot peening.
We studied sound generated by a diagonally arranged fin in a uniform flow. We set 2-dimensional computational model which neglected spanwise effect of the fins, and performed direct simulation of aerodynamic sound for two types of fins whose difference is the width of the back section with the finite-difference lattice Boltzmann method. Conditions of numerical results in which strong resonance occurred consisted with experimental results and Parker type resonance appeared. When the resonance occurred, the frequency of Kármán vortex shedding from the trailing edges of the fins agreed with the natural frequency of air columns which correspond the space between neighbouring fins. The phase differences between the neighbouring columns were completely “anti-phase” and the same was true for the vortex shedding. We also show the temporal and spacial variations in far sound field which are caused by the asymmetric arrangement of the fins. We also noted that the radiations of sounds of two different frequency existed for high speed flow range.
In recent years, wind turbines are introduced in wind farms in which some wind turbines are concentrated. When wind turbines are built in contiguity with each other in wind farms, the flow passing through a wind turbine, which is called wake, may flow into other wind turbines. Wake is characterized by a large fluctuation of the wind speed and direction. Flow of wake into wind turbines causes decrease of power generation and increase of fatigue load on wind turbines. Therefore, in order to propose the best arrangement of wind turbines in wind farms, sufficient understanding of wake characteristics is required. Wake is significantly influenced by inflow conditions. Therefore, experimental investigations were carried out in a wind tunnel and the effects of various inflow conditions on wake were considered. From the experimental results, it was found that recovery of wind velocity and expansion of wake deficit area were promoted by turbulence of inflow generated by active turbulence grids. Wake center was deflected from the center line of wind turbine in yawed inflow. Wind shear of inflow generated by boundary layer generation device promoted horizontal expansion of wake deficit area. Also, wake velocity distribution was evaluated quantitatively by wake model using Gaussian function and it showed good approximation to wake distribution in downstream more than 3 times of the rotor diameter.
When a train travels through a tunnel at high speed, large pressure variations, which act on tunnel lining, equipments inside the tunnel, and the train, are generated in the tunnel. To predict these pressure variations, numerical simulations have been developed. Usually, one-dimensional simulations are used for such purposes. Although the pressure variations caused by the pressure waves can be calculated accurately by one-dimensional simulations, they can underestimate the pressure variations in the area very close to the passing train. The resulting accuracy can be increased by using computational fluid dynamics (CFD), but CFD requires high computational costs. Therefore, this paper proposes a three-dimensional but an efficient method to calculate accurately the pressure variation in the area very close to the passing train in the tunnel. It takes into account the distribution of cross-sectional areas of the train nose and treats the flow around the train nose as three-dimensional potential flow, and the upstream and downstream boundary conditions are specified by a one-dimensional simulation in order to calculate the effect of the pressure waves. The results by this method agree well with those of model experiments by using axisymmetric train model although the discrepancy to the model experiments by using actual shape train still remains.
The utility of a dielectric barrier discharge (DBD) plasma actuator as a spread controller for a rectangular jet is investigated. The rectangular nozzle (75×10 mm) is used and actuators are placed on the long sides of the nozzle exit. The unsteady actuation of actuators is performed by changing the modulation frequency, the duty ratio and the phase difference. The flow visualization and the velocity measurements are conducted, and it is found that the spread of rectangular jet is controllable by the DBD plasma actuator. In the case that the actuators are operated in the same phase, the jet width depends on the modulation frequency rather than the duty ratio. The jet width becomes larger than that of base case when the dimensionless modulation frequency is less than about 1.36. In the case that the actuators are operated in the opposite phase, the jet width strongly depends on the duty ratio when the dimensionless modulation frequency is less than about 0.682. The largest spread in xy plane appears when the dimensionless modulation frequency is 0.125, the duty ratio is 10 %, and the phase difference is π. Its modulation frequency is nearly equivalent to 1/8 of the natural frequency of base case. In such a case, the alternative vortex grows near the nozzle exit and the jet width in xy plane becomes about three times larger than that of base case. It is also noticed that the smallest spread in xy plane appears when the dimensionless modulation frequency is 1.59, the duty ratio is 30 %. In this case, the definite vortex shedding is suppressed and small scale structure emerged near the nozzle exit, and the jet width in xy plane becomes about 20 % smaller than that of base case.
The direct numerical simulations are conducted for the backscattering of incident pressure waves from a bubble with the ghost fluid method in order to understand the formation of secondary cavitation in the high intensity focused ultrasound (HIFU). It is shown that the ratio of a bubble collapse time t0 to a characteristic time of wave propagation ts, η = t0/ts, is an important determinant for generating negative pressure region by backscattering. When η is of the order of 0.1, no negative pressures are generated around the bubble and the bubble collapses by the pressure increase due to the incident pressure wave. When η is of the order of 1, negative pressures are generated and an impulse per unit area with negative values takes the minimum although the positive pressure wave by the bubble collapse, which arrives at the negative pressure region, would reduce the growth of incepted cavitation. Also, the collapse time of a bubble takes the minimum when η = 0.733. When η is of the order of 10, high negative pressures are generated in a relatively smaller volume during shorter duration, which may cause the inception of the secondary cavitation. We also evaluate a negative pressure volume Vth and a duration of negative pressure τth associated with cavitation inception. The results also show that the product of Vth and τth, which is an indicator of probability of cavitation inception in the classical homogeneous nucleation theory, takes the local maximum in terms of η: A larger Vthτth suggests a higher probability of cavitation inception.
We experimentally investigate a levitating drop over a moving wall. Between the drop and the wall, a thin air film exists. In this study particular attention is given to examine whether the lift force generated inside the thin air film is dominant force for the levitation. The drop is deposited onto the inner wall of a rotating hollow cylinder in our new experimental setup. The drop levitates at a stable position, where the weight of the drop balances the lift and the drag. We measure the three-dimensional shape of the air film using interferometric technique. We then calculate the lift force by two different methods. One method estimates the lift force from the mass and the stable position of the drop. The other method computes the lift by applying the lubrication theory with finite difference method on the lubrication airflow inside the air film. Note that three-dimensional shape of the air film plays a crucial role for the magnitude of this lift force. We then compare both lifts, which show quantitative agreement. It indicates that the lift force generated from the three-dimensional air film is dominant for the levitation. In addition, we investigate a levitating drop with different wall velocity of the rotating cylinder. We discuss an effect of the wall velocity on the air film shape and the lift. We then obtain two kinds of lifts by the same method. The lifts are compared and again show quantitative agreement.
The flow field of an offset jet is complex and is frequently found in many engineering devices. In this paper, the fluid flow and heat transfer characteristics of two-dimensional offset jet are investigated experimentally. The offset jet is produced by the flow of air which issue from the end of a long parallel channel. The exit Reynolds number Re is changed in 1.5×103 to 7.0×103, and the offset ratio H/h (H : step height, h : channel height) is changed in 0.5, 1.0 and 1.5. The wall shear stress is measured using a micro flow sensor. Flow visualization is carried out using a CCD camera and laser light. The velocity profiles are measured by a PIV system. When the flow at the channel exit is laminar, fluid in the outer region has a counter-clockwise vorticity and fluid in the inner region has a clockwise vorticity, and a lifting-off of the wall jet flow into the ambient fluid is occurred. The Strouhal number of the vortex frequency is almost constant against the offset ratio. The formation of those vortices is not seen at the turbulent flow. Two peaks exist in the wall static pressure, Nusselt number and skin friction coefficient distributions of the laminar flow with H/h = 0.5 and 1.0. The 1st peak appears near the reattachment point, and the 2nd peak appears in the neighborhood of the lifting-off of the wall jet flow. The two peaks coalesce into one at H/h = 1.5. As the offset ratio increases, the reattachment point moves to downstream direction and Nu becomes large both the laminar and turbulent flows. The reattachment point of the turbulent flow moves to upstream direction compared with the laminar flow because Coanda-effect is strengthen.
It is demanded to obtain excellent spray characteristics that is able to obtain excellent combustion characteristics in order to reduce noxious exhaust gas, especially, carbon dioxide, nitrogen oxide and particulate matter. The purpose of this study is to design and develop high-efficiency and high-dispersion injection nozzle for direct injection Diesel engine that is able to achieve lean combustion based on requirements of some automobile makers. In this study, effects of shapes and measurement of nozzle holes of atomization enhancement nozzle, which is affected to internal flow in nozzle hole and disintegration behavior of spray, on spray and flow characteristics were investigated. From these results, it was cleared that in case of the round inlet shape of nozzle hole downstream from the gap, breakup length becomes short about 50 % and spray angle becomes large about two times compared with the sharp inlet shape nozzle hole. Moreover, atomization and dispersion of intermittent spray were improved considerably by using the multi-hole nozzle with the round inlet shape of nozzle hole downstream from the gap under high-ambient pressure at room temperature conditions at before top dead center for direct injection Diesel engine.
The flow fields of lean and rich propane-air and methane-air turbulent premixed flames of the identical conditions of laminar burning velocity and characteristic of turbulence have been closely examined by using a three-color six-beam LDV system. New finding of the present measurements is the now-well-established clear difference between the turbulent flame structure of the rich propane flame and the others. Hypothesized in an earlier paper, on the basis of measurements of flamelet motion, the present work verifies the existence of this phenomenon through measurements of gas velocities. The data for the rich and lean methane flames are essentially the same, not only are the burnt-gas-conditioned radial velocity components for the rich propane flame higher than those for the methane flames, but also the same conditioned values for the lean propane flame are appreciably lower than those of the methane flames. When the deficient reactant has a higher diffusion coefficient it will diffuse preferentially to turbulence-generated wrinkles, thereby increasing the local burning velocity there, with a resulting positive increment in the turbulent burning velocity, while if the deficient reactant has a lower diffusion coefficient, its diffusion to a wrinkle is preferentially retarded, thereby decreasing the local burning velocity and contribution a negative increment to the turbulent burning velocity. Preferential diffusion, thus, exerts measurable influences on turbulent flame structures in the reaction sheet regime.
Humans shake hands as a sign of greeting when they first meet, to greet one another and develop a rapport. A handshake is an embodied interaction through physical contact. In the case of a human and robot, the robot can smoothly begin to communicate and coexist with humans without eliciting feelings of aversion on the part of the humans, provided it generates a handshake motion that is emotionally acceptable to humans. Therefore, in this paper, we develop a handshake robot system that generates a handshake request motion during active approach to a human. First, we analyze handshake motions with approach between humans. Then, based on the analysis of handshake motions between humans, a handshake request motion model which is generated during an approaching motion is proposed. Furthermore, using the proposed model, a mobile handshake robot system is developed. This mobile handshake robot system actively approaches a human, and it generates a handshake request motion by extending its hand to the human. The developed handshake robot system is evaluated using a sensory evaluation to analyze handshake motion preferred by humans. Based on the sensory evaluation results, the developed mobile handshake robot system satisfactorily generates the handshake request motion during active approach to a human, and its effectiveness is demonstrated.
Robots with independent four-wheel steering have many advantages such as high mobility, energy efficiency and strong stability. They can move toward arbitrary direction by conforming the wheel velocity to the velocity field of the locomotion. If the steering angles are limited, or if the instantaneous center of motion passes through the steering axis, however, abrupt turn of wheels may appear. It requires unacceptable load torque and the steering mechanism may be damaged. To avoid rapid steering, in this study, we propose a tracking control method for robots having independent four-wheel steering with limited range of steering angles. We use a model predictive control based on the model with the steering and wheel velocity dynamics which explicitly deals with the limitation of the steering angle. We conduct experiments on two trajectories; S-shaped curve and V-shaped turn. In the S-shaped curve, the steering angle has to turn over due to their limitation, and in the V-shaped turn, the instantaneous center of motion passes through the steering axis; both of them may cause discontinuous steering in the conventional methods. Comparing with the conventional method, the explicit advantage of the proposed method is that the continuity of the steering angle and limited wheel velocity is guaranteed. We implement the proposed method into an embedded CPU on an experimental robot to verify the efficacy and feasibility of the proposed method.
Soft soils cover on planetary surfaces, so the wheels for exploration rovers easily slip. Understanding an interaction between a wheel and soft soils is important for a traction control to improve rover traversability. The interaction between the wheel and soft soils has been studied in a field of terramechanics. Since the classical terramechanics-based wheel model considers only a static state of a wheel sinkage, the wheel model is not applicable to the wheel sinkage and slip. Thus the dynamic normal stress model and shear deformation model were proposed to deal with the problems of the wheel sinkage and the slip. The dynamic normal stress model was proposed by considering the wheel sinking velocity and a variation of soil state for solving the problem of wheel sinkage. And the shear deformation model was proposed by considering the shear characteristics for solving the problem of wheel slip. The shear deformation model was formulated by the shear test. The simulation verified the validity of the dynamic normal stress model and the shear deformation model in the transient state. In this paper, a single wheel experiments was performed to evaluate the shear deformation model by comparing the simulation results and the experimental results. Then the characteristics of the wheel sinkage and slip and the effectiveness of the model were confirmed.
In this paper, a new type of small seismic isolation table using coil springs, which has a simple construction and the capability of vibration isolation in every horizontal direction, is proposed. A table board supported with roller bearings is pulled almost vertically toward a base board with four coil springs. The coil springs give horizontal restoring force and friction force to the table board when the table moves relatively to the base board. The trial small seismic isolation table is manufactured, and the resisting force characteristics are measured. The numerical results are derived theoretically and compared with the experimental results. Harmonic response test and seismic response tests are carried out by using a shaking table in order to confirm the effect of vibration isolating under some earthquakes that have several periodic component. The experimental and calculated results show that the maximum response accelerations of the table board with a loaded mass decreased to about 1/10 ~ 1/12 compared to those without the isolation table.
The fixed points theory is applied for the dynamic absorber attached to two degree of freedom system with different mass and stiffness. In this study, the case that the dynamic absorber is connected to the excited mass which is far from the base is considered. The frequencies of fixed points and the ratio of natural frequencies to equalize the amplitudes at fixed points are analytically derived, in case that the responses at fixed points are in phase. The damping coefficients which make fixed points extremal value are also obtained. It is found that some ratios of mass and stiffness have no fixed points with same amplitude in the frequency response curve of unexcited mass. But the fixed points always exist in the frequency response curve of excited mass. Furthermore, mass and stiffness ratios which equalize the amplitudes of all fixed points are obtained. For the frequency response curve of unexcited mass, the stiffness ratio that equalizes the amplitudes of all fixed points is uniquely determined for arbitrary chosen mass ratio. But for the frequency response curve of excited mass, the mass ratio changes the number of the stiffness ratio that equalizes the amplitudes of all fixed points into two or zero.
The vibration control of 5 degrees of freedom spring-mass system as a simple model of the five-layer building by applying delayed feedback force based on continuous system assumption was investigated. The followings are made clear. 1) By applying delayed feedback based on continuous system assumption to a single d.o.f. system is equivalent to adding half-infinite system, and that virtual half-infinite system (VHIS) has characteristic of low pass filter. 2) By adding a support layer that has ten times smaller cut off frequency than the first layer, a clumped boundary become a quasi free boundary. By adding VHISs to both end in addition to adding the support layer, the amplitude enlargement is avoided as follows: (1) If the excitation frequency is lower than a lower cut off frequency among VHISs, the traveling wave passes through both end. Therefore, the standing wave doesn't occur. (2) If the excitation frequency is between a lower and a higher cut off frequency of VHISs, the traveling wave reflects at the end where the VHIS that have lower cut off frequency is attached, but the reflected traveling wave almost passes through at the other end. Therefore, the standing wave is occurred, but the amplitude of the standing wave doesn't enlarge.
Recently, it is expected to develop an autonomous robot working in a living environment. Motion planning is very important for an autonomous mobile robot, but kinematic constraints and dynamic constraints are generally solved separately in conventional motion planning. In this research, a simpler way of deciding the control input for an autonomous mobile robot, which is described by a highly nonlinear model in a multi-dimensional space, is proposed by solving kinematic constraints and dynamic constraints simultaneously, under the kinodynamic motion planning based on a harmonic potential field (HPF). In this paper, a quadrotor that is very attractive as an aerial robot due to its high maneuverability, is assumed to be a controlled object, and it is aimed at guiding the quadrotor to an arbitrary target point while avoiding obstacles. Then, three types of controllers for kinodynamic motion planning based on an HPF, which were developed for point mass control, are extended to be applied to the quadrotor. The extended controllers are compared each other in trajectory, amplitude of attitude, and arrival time through some flight simulations. Moreover, multiple gains included in the proposed controllers are optimized automatically by using genetic algorithm (GA), in order to realize highly accurate control. Flight simulation in an untrained environment, which is different from the environment that the gains were selected by GA, is also conducted, and it is confirmed that the quadrotor can move onto the target point with the same gains while avoiding obstacles.
In this paper, time domain mutual mean compliance is proposed to reduce transient vehicle interior noise caused by discontinuous impact force from road surface. The interior noise is caused by coupling of structural vibration and acoustic modes. Therefore it is difficult to find an efficient design to attain light weight and comfortable interior noise performance. In frequency domain noise and vibration problem, by applying frequency domain mutual mean compliance to vibro-acoustic system, it is possible to separate the sound pressure into the contributions of structural system, acoustic system and coupling effect between structural systems and acoustic systems. Moreover mutual mean compliance shows not only contribution but also sensitivity of structural system, acoustic system and coupling effect, coincidently. Consequently, most sensitive part for reducing sound pressure without weight increase can be detected. In this paper, to reduce transient interior noise, mutual mean compliance was applied to time domain problem. The time domain mutual mean compliance can be calculated by using inverse fourier transform, but its application is restricted to linear system. To overcome the restriction, this paper presents a formulation of time domain mutual mean compliance based on central difference method that is a one of the numerical integration method. And it is shown theoretically that contribution and sensitivity of structural components to the transient interior noise can be evaluated by using proposed time domain mutual mean compliance. As an application, time domain mutual mean compliance is applied to a simple automobile body model and countermeasure for transient interior noise that attain light weight also is detected.
This paper proposes a new control system for active mass dampers. The control system is a feedback system, which combines a single neural oscillator and a position controller. The output of the neural oscillator synchronized with the structure response is a rhythmic command which decides the driving direction of the auxiliary mass, and a special map plotted by periodic solutions of the oscillator determines the travel distance of the auxiliary mass in comparison with the current state of the neural oscillator affected by the structure response. In addition, in order to move the auxiliary mass to the desire value, the position control system consisting of a PD controller is used. As a result of numerical simulation, when the structure was quaked by the several types of the earthquake, the structural vibration was reduced by the effect of the auxiliary mass' motion, and the results showed that the proposed system was verified as the controller for the active mass dampers and was able to be used to solve the stroke limitation problem of the active mass dampers.
In this paper, the authors have developed a new type of horizontal seismic isolation system which has large effect of vibration isolation for ordinary earthquakes and suppresses the resonance of the isolation system due to long-period ground motions. This seismic isolation system is composed of coil spring and two slide rails. Further, an optimal frictional force is added to this system. The seismic isolation system adding the optimal frictional force is effective for suppressing the vibration of this system caused by short-period earthquakes and long-period earthquakes. Frictional force is used to suppress the resonance of the seismic isolation system. The trial seismic isolation table was made, and the effects of vibration suppression of the isolation table were discussed experimentally and numerically. In addition, we discussed the relation between optimal friction coefficient and maximum acceleration of the earthquake. We defined a parameter α as percentage of low frequency component in frequency response of earthquakes. As a result, it is shown that the optimal friction coefficient is in proportion to the corrected maximum acceleration of earthquake using parameter α.
Electromagnetic shunt damping is a sensor-less passive damping technique using an electromagnetic actuator. The accurate values of the parameters of the system are essentially required for designing a controller in the damping technique. This paper proposes a parameter estimation method of an electromagnetic actuator attached to a mechanical structure in order to use for electromagnetic shunt damping. The electromagnetic actuator attached to the structure is modeled as the system including the mechanical and electrical systems which are connected by the electromechanical coupling coefficient. This paper points out a remark on the estimation: The frequency response of the electrical admittance especially neighborhood the natural frequency of the mechanical structure shows an electro-mechanically resonant feature, which does not appear in the pure electrical system without the electromechanical coupling. By applying least squares method to the frequency response data of the electrical admittance neighborhood the natural frequency, the parameters of the mechanical system and the electromechanical coupling coefficient as well as the electrical parameters can be estimated. The proposed estimation method requires only measurements of the frequency response of the electrical admittance across the terminals of the electromagnetic actuator. Therefore, both the parameter estimation and the electromagnetic shunt damping are possible to perform without any displacement or velocity sensors, or any additional actuators. In order to verify the effectiveness of the proposed method, the experiments of parameter estimation and of electromagnetic shunt damping are performed. The experimental results show that the proposed method is effective to estimate the parameters of the electromagnetic actuator without use of any other sensors.
In human gait locomotion analysis, which is one useful method for efficient physical rehabilitation to define various quantitative evaluation indices, ground reaction force, joint angle and joint loads are measured during gait. On the other hand, the analysis of the correlation in the recorded joint motion has extracted a few simultaneously activating segmental coordination patterns in a past study. Moreover, it is thought that the structure of the intersegmental coordination is attracting attention to an expected relationship with a control strategy. However, this procedure has not been applied to trans-femoral prosthetic gait locomotion yet. In this paper, joint angles as kinematic parameters applied on the lower limb of healthy subjects and trans-femoral amputee with a prosthetic limb during their gait locomotion are investigated by performing the experiments of gait measurement. Next, joint angles are analyzed by applying the evaluation method of intersegmental coordination pattern using singular value decomposition to data of joint angles as the experimental results and trajectories of center of gravity are obtained. Then, mutual comparative verification and quantitative evaluation of them as constitutive principle is performed. As a result of the experiments and consideration, the effectiveness of the method using singular value decomposition is validated because it can quantitatively express comprehensive physical phenomena for trans-femoral prosthetic gait. Obtained locomotion patterns may be useful for refining the rehabilitation program of trans-femoral amputee.
In this paper, we demonstrate the improvement in drawing stability and throughput of scanning probe lithography (SPL) based on anti-wear probes. In order to improve the stability of SPL, we conceive of a novel anti-wear probe to improve the wear resistance of the probe. The tip of the proposed anti-wear probe has a uniform-cuboid shape, which consists of a microscale mechanical contact and two nanoscale electrical contacts (sidewall electrodes) formed on the sidewall of the mechanical contact. The microscale mechanical contacts reduce the tip wear by dispersing the force applied to the tip, and the nanoscale electrical contacts enable the drawing of nanoscale features. The uniform shape of the probe tip enables the probe to maintain its stable performance, even when it is mechanically worn. This probe is found to be able to maintain stable performance for a total drawing length of 2 m, which is an improvement of several thousand times over a conventional probe. Then, we improve the probe design by introducing an eave portion to the tip to ensure mass-production compatibility for enabling of multi-probes while maintaining the high wear resistance. The improved probes are found to be effective in simplifying the fabrication process and reduce fabrication cost. Eight linearly arrayed anti-wear probes are fabricated, and improvement in throughput of SPL is demonstrated.
This paper presents a numerical analysis of adhesion contact due to meniscus between a sphere and a flat considering the elastic deformation of the contacting surfaces. Analytical model and basic equations for numerical analysis are explained first. Meniscus contact characteristics are presented for a 2-mm-radius glass contact on a magnetic disk coated with submonolayer mobile lubricant, and 2-μm and 20-nm-radius asperity contacts on mobile and bonded lubricant layer with a low elasticity. It was found that the sphere-flat contact with submonolayer liquid meniscus shows Derjaguin-Muller-Toporov theory-like behavior to Johnson-Kendall-Roberts theory-like one as the mobile layer thickness decreases from 1 nm to 0.3 nm. There is a critical liquid film thickness below which the meniscus length becomes zero so that the meniscus liquid cannot be transferred to the mating surface. This numerical method can be used for the rigorous analysis of various meniscus adhesion contact problems. Some of the experimental adhesion characteristics between a glass sphere and a magnetic disk are discussed from the aspect of the calculated results of elastic meniscus contact.
Lithium-ion battery is a rechargeable battery with high energy density, and it is fabricated by laminating of electrodes with separator. In fabrication process, it is important for evaluation of contact state of laminated electrodes to estimate current density between the electrodes. This paper describes a novel technique to estimate the current density by using magnetic sensor. This technique applies an inverse analysis on magnetic flux density induced around the lithium-ion battery impressed with inspection current. In the inverse analysis, boundary element method for thin plate is applied to derive the observation equation relating the current density to the magnetic flux density. Then truncated singular value decomposition is applied on the observation equation. In order to demonstrate the validity of the proposed technique, numerical simulations have been performed by using a model consisted with the electrodes and separator. In the numerical simulations, the correct distribution of the current density was given in advance, and the direct analysis was applied to obtain the simulation data of the magnetic flux density. Then the inverse analysis was applied on the simulation data. The results show that the correct distribution of the current density can be obtained by the proposed technique. In addition, though the estimation accuracy is lower when fewer number of decimals of the magnetic flux density data is utilized, the tendency of the correct distribution can be obtained due to the truncation of the rank of the singular value matrix.
The purpose of this study is formulating the reduced integration method of damage elasto plastic constitutive model with divided back stress based on full implicit framework. In the present formulation, after indicating elasto plastic constitutive model with damage divided back stress, the reduced return mapping equation with consistent tangent stiffness is introduced. The proposed formulation is tested in tensile hole plate and cyclic bending bar for verification.
This study proposes an evaluation model of business value which provides information for more reliable decision making considering its uncertainty, to create strategic options of product development projects which involves various uncertain factors throughout the life cycle stages. In order to support the modeling process of the reverse profit-loss calculation, this paper proposes a calculation method of business value based on empirical relationships between the variables by classifying uncertain variables and fixed variables, and via analyzing dependency between variables using Design Structure Matrix method. The value of the product development project is evaluated as EPV (expected present value) and NPV (Net Present Value). A generation method of the strategic options and project activities is proposed based on the calculation of EPV and NPV. A portfolio method is presented to select best strategic options which make largest project value. The proposed method enables a project manager to compare the strategic option's overall profit by calculating its cost and income. Proposed models and methodology is applied to a product development project its name is i-painter. The i-painter means a new wall-repairing robot for maintaining building structures in developing countries. I-painter is mechatronics machinery which has new function, new structure, and new market. A prototype of i-painter is developed and evaluated. By estimation of the project value of i-painter, contributions of applying proposed model are confirmed. The application result shows that the proposed method can help the project manager to (1) select best strategic options, and (2) quit the development project with less cost from early lifecycle stage.
In manufacturing industries, a demand for high value-added products has been increasing. It is important to establish a new way of creating value-added products, such as craftwork objects or applied arts, different from traditional way of achieving high quality and low price. Such a machining technology that enables (1) extremely complex or small shape generation, (2) machining of hard or soft materials, and (3) machining of difficult-to-grasp or fix workpiece may be called “Dexterous Machining”. Previously, “Dexterous Machining” is proposed for soft objects such as rubber by employing an aqueous solution of sodium acetate to fix a workpiece and to improve the stiffness. However, the method has not been applied to porous and soft objects like sponge. Porous and soft objects are much more difficult to machine compared to non-porous ones due to their inner numerous holes. Thus, the study deals with the first trial of machining the porous and soft objects without specific equipment. As a result of conducted experiments, it is found that a impregnation of the aqueous solution of sodium acetate is able to be applied to precisely machine porous and soft objects. These results expanded the potential of usage of the aqueous solution of sodium acetate and “Dexterous Machining” of porous and soft objects.
Windage loss may become more than 10% of all losses when large sized gearing runs fast. In order to reduce the windage loss, it needs to vacuum a gear box because it is proportional to the density of ambient air. The study proposes a helical gearing unit in which interior air is discharged due to mesh process as like as a gear pump, and investigates the performance experimentally in terms of depressure level, power loss and temperature rise due to heat generation. The pressure in the gear box got to - 0.08MPa under appropriate condition, but the temperature rose up to about 200°C. Losses were measured and found to consist of four types in self-vacuuming: mechanical loss, windage loss, pressure difference loss, and turning flow loss. Among them pressure difference loss was the most marked part which is due to the gears rotating against pressure difference between high and low pressure atmosphere, or the beginning of engagement and end of it, respectively, in the gear box. Furthermore existence of turning flow loss was confirmed due to circulation flow in the wide exhaust opening volume, and it was eliminated by changing the exhaust port to such as an axial narrow hole. The temperature rise was proven to the effect of adiabatic compression and corresponding energy dissipation. It was verified by the calculation based on the typical thermal dynamics at tooth space which consists of isovolumetric, isobaric, and adiabatic changes. By calculating the required kinematic work of this cycle, the result matched with the pressure difference loss. Furthermore a small external vacuum pump can collaborate to assist reducing this pressure difference loss.
Most modern transportation vessels are powered by fossil fuels. In recent years, however, as fossil fuels have become depleted and atmospheric pollution by exhaust gases has become a problem, demand has increased for technologies that will allow conservation of fuel and more efficient use of energy. About 35% of the energy in the diesel fuel used by the main engines of large ships is squandered as heat in the exhausts. Other than the power recovered and utilized as a source for superchargers and exhaust gas economizers, almost none of this is being used. If electricity could be generated using these exhaust gases, this would allow shorter operating times for the generating equipment on ships and would contribute to conserving energy there. The authors have begun developing a new version of the steam engine, which, in its conventional form, has employed a grooved cam. However, this steam engine has a maximum output of 60W and its mechanical efficiency is 16%; its output and mechanical efficiency must therefore be raised. The authors' answer to this challenge was to conceive a new type of steam engine using a different cam called a crowned cam. The objective of this study was to develop a steam engine based on a crowned cam that can provide power with low-pressure steam. This report begins with a description of the mechanism and operating principles of the steam engine. This engine uses the crown cam as a motion conversion mechanism to transform linear motion into rotational motion. Next, the overall structure and the design of the prototype are described. Lastly, the prototype engine was tested for its performance in an experiment. The prototype engine showed a power output of 449 W, at which it had a mechanical efficiency of 53%.
Shape design of composite structures composed of dissimilar materials moves more into the field of vision for designers. In this paper we propose a shape identification method for the interface and/or outside shape design of composite structures consisting of dissimilar thermo-elastic materials under a thermal loading condition. We aim at controlling thermal displacements at a prescribed boundary to target values. The square displacement error norm is minimized by varying the interface and the outside shapes as the design boundary. The shape gradient function derived using the material derivative method is applied to the H1 gradient method. With this method, the optimal interface and outside shape with smoothness can be determined without any shape parameterization. The numerical results of the given examples show that the thermal displacements of solid structures composed of dissimilar materials can be well controlled using the proposed shape identification method, which would be helpful for designing solid structures composed of dissimilar materials.
Manufacturing industry tends to high-mix low-volume production, and it is strongly required to shorten the manufacturing lead time of products. In the field of machining, complex machining by means of multi-tasking machine tools attracts the attention. However, the machining operation is not easy to understand due to the highly complicated machine tool structure. Thus, NC programming for multi-tasking machine tools spends much time and labor. Therefore, it is required for CAPP/CAM system to minimize the effort of NC programming in terms of easily realizing highly efficient machining. Though there are some CAM systems for a multi-tasking machine tool, they generally need long operating time caused by the manual allocation of parts to generate tool paths. In this study, novel machining features are proposed for complex machining by means of multi-tasking machine tools. Proposed machining features deal with several alternative machining methods and contribute directly to the suitable allocation of machining order. Therefore, process planning can be conducted depending on machining strategy considering available cutting tools and the structure of a multi-tasking machine tool. From the result of case studies, it is found that the proposed machining features show the possibility to reduce the effort and to decide the effective machining process of complex machining.
In previous study, we proposed three dimensional motion measurement system which was composed of gyro sensor and infrared sensor to measure golf putter head motion. In this paper, we propose a method to discriminate the shot distance from the rotational and translational motions of the putter head. Rotational and translational motions of the putter head were measured by the proposed system with changing the distance to the cup from the rest position of the ball (Short:150 cm, Middle : 300 cm, Long : 450 cm). Four motion variables affecting the shot distance were selected by cluster analysis as follows: (1) The minimum displacement in the X axis direction before the impact, (2) The maximum displacement in the Y axis direction at the impact, (3) The angular velocity around the z axis at the impact, and (4) The angle around the x axis before the impact. The canonical discriminant analysis was used to distinguish among the shot distances. Objective variable was 3 kinds of the shot distances, and explanatory variable was 4 motion variables. As a result of the canonical discriminant analysis, accuracy rate was 93.4%. Next, the subjective data which isn't used for calculation of a discriminant was substituted for canonical discriminant equations. As a result, in short distance, the accuracy rate of all subjects was 100%. On the other hand, in the middle and long distance, the highest accuracy rate was 100%, and the lowest accuracy rate was 50%. In addition, the angular velocity around the z axis at the impact greatly contributed to shot distance.
In order to improve the activities of daily living effectively, patients with gait problems need to decrease the loads which they apply on handrails of support devices, and also need to use support devices that don't restrict their activities as much as possible. It is essential for the patients to recognize to what extent they apply loads on handrails while they work on gait training because the goal is to decrease those loads. The purpose of this study is to develop a system for helping the patients decrease the loads on handrails, and to ensure the effect of the developed system through ten-meter walking test. The developed system consists of a load measurement unit on handrails and a visual feedback unit. For supporting the patients with severe gait problems, a relief unit is also developed and attached to the system. Ten-meter walking test was performed with three patients with gait problems in order to get fundamental knowledge of the effect of the system. As a result, all of the patients were able to decrease the loads with the help of the developed system. Moreover, after completion of the walking test with the system, all of the patients were able to maintain the decreased loads on handrails during ten-meter walking test although they didn't receive the visual feedback from the system. These results suggest that the developed system has the immediate and longitudinal effects for helping the patients decrease loads on handrails.
The purpose of this study is to investigate the effect of fabrication conditions for α-Fe2O3 based thermoelectric conversion elements. It was demonstrated that the open circuit voltage of α-Fe2O3 thermoelectric conversion elements could be enhanced by decreasing the load current density used in production of the film by anodic oxidation. α-Fe2O3 films were fabricated under various oxidizing condition in an aqueous solution of FeCl3, KF, KCl and H2O2 at the temperature of 50 °C. The load current density and oxidation time were varied. The amount of α-Fe2O3 in the α-Fe2O3 film, the crystal quality and the crystal grain size of the α-Fe2O3, were evaluated. In terms of the maximum value of the open circuit voltage, the best film thickness of the α-Fe2O3 film was found to be about 40 ~ 50 μm. α-Fe2O3 films with greater crystal quality and larger crystal grain size can be fabricated by decreasing the load current density. These improvement on α-Fe2O3 thermoelectric conversion elements lead to more powerful thermoelectric conversion element, i.e., higher open circuit voltage.
Approximately a third of the traffic accident fatalities in Japan are caused as a result of accidents while a person is in a vehicle. Collision from the frontal direction accounts for 53 percent, a much higher percentage than accidents involving collisions from other directions. In Japan, laws concerning collision from the front direction are defined in the Safety Regulations: Full frontal rigid barrier impact test and Frontal offset deformable barrier impact test. We focused on these two tests and studied over 50 cases to research the degree of injury value during tests at the time of certification. In Full frontal rigid barrier impact test, we observed little difference between the average injury values for the driver and passenger. In Frontal offset deformable barrier impact test, the values were higher for the driver than the passenger when comparing the average injury values of the head and chest. In Full frontal rigid barrier impact test and Frontal offset deformable barrier impact test, the average chest injury value was higher compared with the average head injury value. For head injury criterion, the average value for Full frontal rigid barrier impact test was higher compared with the average value in Frontal offset deformable barrier impact test. For both the Full frontal rigid barrier impact test and the Frontal offset deformable barrier impact test, we observed that the heavier the test vehicle weight, the higher the decrease in the injury value.
A model of statistical energy analysis (SEA) of railway carbodies was developed to predict interior noise in rolling stock. Since the carbody shell is made of double skin structures of extruded aluminum and their coupling loss factors (CLFs) cannot be easily estimated from theoretical equations, sectional finite element method (FEM) models of the carbody shell were used to calculate CLFs between each SEA subsystem. The whole carbody shell was modeled as SEA subsystems using these CLFs, and interior panels and the passenger rooms were also added as SEA subsystems to the carbody shell model. The input power of an operational device was then calculated from measured acceleration data to simulate interior noise in the passenger room due to the operational device located under the carbody. Calculated input power was applied to the SEA model, and it was found that the simulated vibration level in the carbody, as well as interior noise in the passenger rooms, agreed well with the experimental results.