To increase the noise proof performance of a cover with aperture excited by diffuse acoustic fields from the outside, it is a problem to prevent the occurrence of the inner acoustic mode at the lower frequencies. Authors had suggested the feed forward active noise control (ANC) for the acoustic field inside the cover. Diffuse acoustic field excitation experiment using reverberant room has been examined to comprehend acoustic characteristics inside the cover. The results show that the inner cover field is in the state of locally coherent at the frequencies of inner acoustic mode, so that it is good environment for the active noise control. Then, a calculation with two-dimensional finite difference time domain (FDTD) method has been done to examine the feasibility of feed forward ANC. The results show that it is possible to realize ANC for the acoustic field inside the cover by proper design of control filter. Finally, experimental measurement of diffuse acoustic field excitation in the reverberant room has been done again to examine the ANC with the design method mentioned above. The results show that feed forward ANC can reduce noise level by 5dB at the peak frequency caused by the inner acoustic mode. Furthermore, the inner acoustic pressure distribution is also reduced uniformly at the frequency. Therefore, it is concluded that it is possible to realize feed forward active noise control for the acoustic field inside the cover with aperture excited by diffuse acoustic fields from the outside, even if the excitation is random or the causality of I/O is not satisfied.
Demands for machining of three-dimensional (3D) complex geometries over a large area with nanometer scale accuracy have recently increased in the various industrial sectors. In order to meet such requirements, it is necessary to realize not only a machine tool with nanometer scale machining accuracy, but also a coordinate measuring machine with a nanometer scale measuring resolution for evaluating the machined parts profile. A scanning tunneling microscopy (STM) and atomic force microscope (AFM) probes have a high measuring resolution. However, in the STM, the specimen to be measured needs to have conductivity, and the AFM cannot measure a step shape or a slope. It is thought that the application of the profile measurement by the AFM probe can be expanded, by development the AFM probe suitable for the measurement of the slope shape. Therefore, this study proposed a novel AFM probe suitable for measuring the slope shape by using a low rigidity spring. In addition, the basic characteristics of the proposed AFM probe was experimentally investigated. Investigation results confirmed that the proposed AFM probe can detect atomic forces acting between the specimen and the probe.
The Impact damper with granular materials has a high damping effect for wide frequency range and it is used in many fields. Many researches have been made on the prediction of the damping effect of this damper on one degree of freedom spring-mass system. But it is more useful to be able to predict the damping effect when applied to a real complex structure. For this purpose, numerical modeling of damping effect of an impact damper is important for efficient design of structures set with dampers. In this paper, the granular materials are modeled as one mass point of restitution coefficient of zero that undergo displacement vibration excitation, and the motion of this mass point is theoretically analyzed for the case of vertical vibration and one side collision. From these results, we propose a method for obtaining the macroscopic damping effect of the impact damper with granular materials. This is obtained as a nonlinear equivalent mass ratio and nonlinear damping coefficient with amplitude dependence. Further the excitation experiment which identified the damping characteristic of the damper was carried out. Theoretical solution and experimental result show the good coincidence.
This paper proposes identification method of excitation force of rigid body vibration source by physical model identification. If the reworking occurs after the assembly of the prototype in mechanical product, the cost increases due to the retrofit countermeasures and development period extension. Pre-prediction of vibration at the design stage is important to avoid these problems. Prior prediction of vibration needs to grasp the excitation force of the vibration source. As conventional methods, the mount stiffness method and the matrix inversion method have been proposed. However, mount stiffness method calculates the mount transmission force. Therefore, if the development machine changes the structure, preliminary evaluation does not apply. The matrix inversion method can solve this problem. However, when the frequency response function contains a measurement error, the error spreading propagates in inverse matrix calculation. Therefore, in order to avoid the inverse matrix calculation, we propose identification method of excitation force of rigid body vibration source by physical model identification. In this paper, it was investigated features of the inverse matrix method and the identification method of excitation force by physical model identification using the basic experiment. As a result of study, the method by physical model identification showed that the influence of measurement error is smaller than the matrix inversion method. In addition, it showed that it is possible to identify the excitation force with fewer excitation points than the matrix inversion method.
Although bladed disks of turbomachinery are nominally designed to be cyclically symmetric (tuned system), the vibration characteristics of all blades on a disk are slightly different due to the manufacturing tolerance, the deviation of the material property, the wear during operation, and so on. These small variations break the cyclic symmetry, and split the eigenvalue pairs. The actual bladed disks with the small variations are referred to a mistuned system. Many researchers have studied mistuning, and main conclusions are while mistuning has an undesirable effect on the forced response, it has a beneficial (stabilizing) effect on the blade flutter (the self-excited vibration). Although such mistuning phenomena of bladed disks have been studied since 1980s, almost all studies focused on the amplification factor of the displacement response, and few studies researched the amplification factor of the vibratory stress response. Therefore, in the previous paper, authors studied the amplification factor expressed by the vibratory stress for the lower modes of the bladed disk, using the simple assumption. In this study, the mistuning effect expressed by the vibratory stress for the lower and higher modes are examined, using the reduced order model without any assumptions. First, formulation for evaluating the mistuning effect expressed by the vibratory stress is derived, using the reduced order model SNM (Subset of Nominal Modes). Second, the frequency response analysis of the mistuned simple bladed disk consisting of flat plates is carried out systematically. Finally, comparing the amplification factor of the displacement response with that of the vibratory stress response including the synthesized stress (Mises stress and the principal stress), mistuning phenomena expressed by the vibratory stress are clarified.
In this paper, dynamic stability analysis methods of a beam subjected to a confined annular axial flow are dealt with. Such structures are submarine resources production pipeline, reactor core structures of nuclear power plants, high-speed trains passing thorough a tunnel, a piping system in the field of ocean mining, and so on. The relation between the annular axial flow velocity and the unstable dynamics of structures are clarified. We have compared two analysis methods which can evaluate the dynamic instability of such structures. In first analysis method, the fluid is treated as viscous fluid, and is governed by the Navier-Stokes equation, and the beam structure is treated as the Euler-Bernoulli beam. This is called as the viscous fluid solution namely NS solution hereafter. In second analysis method reported by (Rinaldi and Paidoussis, 2012), the fluid is treated as ideal fluid. Then the viscosity effect is added to the equation of motion. This is called as the ideal fluid solution namely R&P solution hereafter. The complex eigenvalue analysis of the fluid structure coupled equation of motion is performed in order to clear up the dynamic instability. Performing the parametric studies, the comparison between both solutions is investigated. When the fluid viscosity becomes large, the difference in the critical velocity between the viscous fluid solution namely NS solution and the ideal fluid solution namely R&P solution is found to be generated. The destabilization effect appears due to the fluid viscosity force terms of the added stiffness of the fluid-structure coupled equation only in the viscous fluid solution.
Recently, proceeding of the aging society has encouraged research and development of power assist systems. The authors' research group studies on the assist system control using an assist cart as a rollator. The merit of the proposed system is the aging people walk by themselves using the cart as the assisting tool and it helps anti-aging. Most serious problems of the proposed system are the avoidance of fallings and collisions without losing operability. To solve the problem, this paper proposes the remote control system taking operators' safety and operability into account. The remote control has a possibility of the establishment of the cost-effective multiple target control systems by reducing the requirement for each control target system. However, because of the limitation of communication data capabilities, the controller cannot grasp the state of the controlled object completely. To grasp the state and keep the safety, the authors apply an evaluator in the remote control system. It detects the effect of the uncertainty and keeps the controlled object safe. In addition, as an interface for the users to avoid the collisions, this paper applies the stiffness control. Introducing the virtual spring into the control system, the proposed system prevents the controlled object to collide the obstacle, without losing operability. Based on an application example for the one-dimensional assist rollator collision avoidance, this paper reveals the practicality of the proposed system by conducting experiments and the simulations. The result shows the proposed way is one of the effective ways for applying a remote control system to the assist system problem.
We investigated the damping mechanism of a granular material damping system applied to reducing vibration in structures that have a high natural frequency and small vibration displacement. Experiments were conducted under several conditions of total mass of granules. We also constructed a computational model of a single-degree-of-freedom vibration system with a granular material damper to study the mechanism of a granular material damping system. On the basis of the fundamental idea that the damping effect of a granular material damper is governed by the motion of the granules, we classified the granular materials as “relative motion mass” and “equivalent added mass” in the translational motion and as “rotating mass” and “not rotating mass” in the rotational motion and then considered the relationship of these mass classes to the damping characteristics. In this report, we examine the relationships of the motion of the granular materials, “relative motion mass” and “rotating mass”, and damping ratio by means of experiments and calculations for structures that have a high natural frequency and small vibration displacement.
A reduction method of engine sound disturbance for on-board power spectral measurement of tire sound is proposed and its validity is evaluated. The proposed method employs two microphones; one is mounted in the engine compartment, and the other in the wheel well of the vehicle. At first, the sound propagation characteristics between the two microphones are discussed. It is shown that the complex coherence between the engine sounds obtained with two microphones are very low. On the other hand, the power coherence takes about 0.4 within the frequency range from 0 to 15 kHz. These imply that the sound does not propagate linearly between the two microphones, but the power spectra of microphones correlate each other. Next, the power spectra of the sound measured with each microphone are calculated and the power spectrum of the tire sound is extracted by the calculation with the two spectra based on a pre-identified transfer function between the two microphones. The calculated power spectrum of the tire sound depends on the driving conditions of the engine and its large variance is not acceptable. This may be caused by the error of the pre-identified transfer function. Then, the modified transfer function is determined and the power spectra are calculated again. As a result, the variance of the power spectra becames lower than previous results and thus, the validity of the proposed method is confirmed.
Gait measurements and physical fitness tests are carried out in the community health activities for health promotion and care prevention services in the growing elderly population. In particular, the timed up and go test (TUG) is the clinical test most often used to evaluate functional mobility in many clinical institutions or local communities. To evaluate the functional mobility during the TUG, a gait measurement system (Laser-TUG system) using a laser range sensor (LRS) has been proposed. The system tracks both legs and measures the foot contact positions to obtain walking parameters such as stride length and step length. To reduce the false tracking and improve the measurement accuracy during the turning phase of the TUG, a data association considering gait phase and a spline-based interpolation have been proposed. However, the false tracking is likely to be occurred in the elderly and the measurement accuracy during the turning phase is still deteriorated because of occlusion and inaccurate observation of legs. Therefore, this paper presents a high-accuracy gait measurement system using multiple LRSs. Using multiple LRSs is able to reduce the situation of leg occlusion. However, the measurement accuracy of leg position depends on the distance from the LRS. To improve the measurement accuracy, an integrated leg detection method by a weighted mean of the observation candidates from each LRS data based on the distance from the LRS is proposed. We confirm that the proposed leg detection method can improve the success rate of leg tracking in the elderly and measurement accuracy of the leg trajectory and walking parameters.
This paper describes a modeling method for predicting a walking route of a pedestrian in a stochastic manner. We consider one of the most typical situations where a pedestrian walks along to a sidewalk, and then some obstacle exists in front of the pedestrian. To represent the walking route of the pedestrian during the avoidance action, a stochastic model is suitable than deterministic one. The stochastic model is derived from the walking experiment where a pedestrian avoids some obstacle in natural walking. Based on the loci obtained from the experiment, the pedestrians walking speed and walking direction at any local area was approximated by Gaussian and Beta distribution function, respectively. As a result the walking route of a pedestrian can be represented in a stochastic manner. The estimated output of the model is examined by comparing with two real walking loci that were obtained from near-miss incident database. One examination scene is avoidance of a parked vehicle, and the other is of parked bicycle on the roadside. By the numerical simulation, we obtained the results that the both real walking routes are included within the 3-sigma ranges of the estimated output of 500 trials.
This paper descries theoretical and experimental research on mechanical behavior of a cylindrical container which is divided into multiple space of an equal size into which one cylindrical rod of the same diameter and material is enclosed. It is clarified that an explanatory variable and a criterion variable which are governed rolling movement characteristics of the cylindrical container. A rotary dumping number that is a dimensionless parameter is defined. Theoretical formulas are introduced for the cylindrical container in which one, two and numerous cylindrical rods are enclosed in none divided space of the cylindrical container. Unfixed coefficients in the theoretical formula are properly identified from experimental results practiced more than one. As a result of investigation, we have found that initial velocity from which a rotary dumping number becomes maximum value exists for the cylindrical container in which numerous cylindrical rods are enclosed in none divided space. Some results are presented in the form of parametric tables and graphs.
This research presents an experimental investigation on the vision performance of a human body which is sitting on an automobile seat. Six subjects were selected from a panel for the experimental research and frequency exposes from 1 to 30Hz sine wave vibration to the subjects by the sweep for 240 seconds with the total amplitude of 2 millimeters. The subjects were measured a standard visual acuity test and a self-rated assessment for difficulties in visual perception every 2 Hz and two subjects of them were measured vertical acceleration for their head in the experimental investigation. From the experimental result, visual efficiency was declined to 49.55 % in the vicinity of the frequency range of 20 Hz. The cause of reduction of eyesight has been considered using the model eye of Gullstrand, and it has been found that the deformation of optic-axis length was 0.257 millimeters when the average eyesight of all subjects was reduced from 1.15 to 0.57. Some results are presented in the form of parametric graphs. The results are useful for improving vehicle ride comfort, maneuverability and safety driving.
We investigated differences in the hydrogen thermal desorption mechanism for Ni-Ti superelastic alloys following hydrogen charging by cathodic charging in a 0.9% NaCl aqueous solution and by immersion testing in a 0.2% APF aqueous solution. For the immersed specimen, the presence of corrosion products on the surface resulted in an upward shift of the hydrogen desorption peak by approximately 100 °C. When the total amount of desorbed hydrogen was almost the same for both specimens, a higher fraction was desorbed at temperatures below 200 °C for the cathodically charged specimen. Furthermore, a larger amount of hydride was formed for the cathodically charged specimen. These results indicate that the hydrogen thermal desorption mechanism depends on the presence of corrosion products on the surface and the amount of hydride formed.
There are many studies reported that a fatigue crack propagated in a tensile mode macroscopically and the fracture surface was mainly occupied by striations in many metals. Whereas, a unique fracture in which a crack propagated in a macroscopic shear direction accompanied by ductile facets was observed in some aluminum alloys under specific conditions. In the present study, fatigue tests of age-hardened Al alloys of extruded 2017-T4 and 7075-T6 were conducted in relative humidity environments of 25% and 85% under rotating bending and ultrasonic loading conditions to clarify the crystallographic feature of a shear mode crack and propose its growth mechanism. Many facets showing a feature of shear mode crack propagation with an equivalent size to the grain size were observed at the fracture surface under both conditions of rotating bending in high humidity and ultrasonic loading irrespective of humidity. In addition, it was confirmed that the angle between the loading axis and the growth direction of the shear mode crack composed a constant value, ~35°, relating to the marked texture in the propagation process of the macroscopic shear mode crack. However, a crack growth rate was lower in the ultrasonic loading than in the rotating bending in high humidity. Based on their differences in occurrence conditions of the shear mode crack, two mechanisms for this unique propagation were proposed as follows; that is, one was a shear mode crack occurred by the promotion of the slip deformation to one direction due to hydrogen generated by reaction of Al alloy with water vapor in high humidity, and the other was a crack by the suppression of the deformation to one direction due to re-welding of crack faces under ultrasonic loading.
Fatigue cracks in some aluminum alloys propagate not in a typical tensile mode with striations but in a macroscopic shear direction with ductile facets under specific conditions. In the previous paper, it was shown that this unique propagation of a shear mode crack occurred in high humidity under rotating bending fatigue and under ultrasonic loading fatigue irrespective of humidity. Two types of mechanism for the shear mode crack were proposed: one is a case that a slip deformation to one direction in cross slip in formation process of striation was enhanced by hydrogen generated in corrosion process of Al alloy in high humidity and the other is that a slip deformation of one direction was inhibited by the re-welding of crack faces in vacuum condition. In the present study, fatigue tests of Al alloys of extruded and drawn 2017-T4 and extruded 7075-T6 were conducted under rotating bending and ultrasonic loading conditions in relative humidity environments of 25% and 85% and in nitrogen gas, to verify the proposed mechanism experimentally and investigate influencing factors on the shear mode propagation. In addition, the effect of change in the testing condition on the propagation behavior of a crack was investigated. Although the microscopic shear mode propagation occurred within grains in both of the extruded and the drawn alloys, the crack propagated to a specific shear direction macroscopically in the extruded alloy related to the strong texture, and the crack propagated in a tensile mode macroscopically in the drawn alloy possessing no texture. These differences in macroscopic crack propagation mode, thus, were caused by the degree of texture. The proposed mechanism was verified by some experiments in various environments. Furthermore the effect of change in testing conditions influencing on the shear mode crack was explained by the results under the constant conditions.
A zirconium alloy cylindrical tube exhibited fracture under high-velocity axial impact load when high yield strength pellets were inserted as reported by Morishige et al., 2016. The fracture occurred after a crack was initiated at the tensile side of the bending tube. In this paper, FE analyses were conducted to clarify the fracture mechanism as well as the deformation behavior. At first, axial tensile tests using tubes with four slit-holes located at the center were performed in order to evaluate the fracture behavior of the tube. Then, digital image correlation (DIC) method was utilized to measure the local strain near the slit-holes. The results showed that the fracture displacement became smaller with smaller slit-holes’ radius. Also, the strain was concentrated at the slit-holes’ tips where cracks were generated before fracture. Subsequently, FE analyses of the tensile tests were conducted by LS-DYNA using the implicit method to obtain the fracture criterion. The load-displacement curve agreed well with the experiment. Then, the relationship between stress triaxiality and equivalent plastic strain near the slit-holes’ area were evaluated to define the fracture criterion. Finally, FE analyses of the axial impact tests using the dynamic explicit method were conducted to compare with the fracture criterion defined by the axial tensile tests. The results indicated that a localized stress and strain might occur at the tube boundary adjacent to pellets. This was caused by the interaction between tube and pellets’ edge which generated a tensile stress condition at the tube boundary when high yield strength pellet was applied. Under this condition, both stress triaxiality and effective plastic strain could increase and eventually lead to the fracture criterion.
The effects of environment temperature on initiation and multiplication of transverse crack in cross-ply carbon fiber reinforced thermoplastic (CFRTP) laminates have been investigated. Static tensile tests for the cross-ply laminates and the 90° unidirectional laminates were carried out at room temperature, 93 °C and 130 °C, respectively. The transverse cracks were observed by soft X-ray photography. The tensile strength and the failure strain in the cross-ply laminates and the 90° unidirectional laminates at high temperature decreased compared to the values at room temperature. It was also found that the behavior of initiation and multiplication of the transverse cracks in the cross-ply laminates was changed due to the environment temperature. The experimental results under different temperature were analyzed by Weibull distribution on the basis of probabilistic model. Next, the energy release rate was calculated due to formation of a new micro crack based on the Weibull distribution. The predicted transverse crack density by Weibull distribution was compared with the experiment result and the reasonability of using Weibull distribution to CFRTP cross-ply laminates under high temperature was verified. It was found that the critical energy release rate of CFRTP laminates has decreased at high temperature and the experimental results showed that the matrix strength was decreased at high temperature. Also, the fiber-matrix interfacial fracture on the fracture surface of the 90° unidirectional laminates was observed in some areas at high temperature whereas the matrix fracture was observed at room temperature. Therefore, it was suggested that the interface strength between polymer and fiber was decreased at high temperature.
The fracture toughness Jc of the material in the ductile to brittle transition temperature (DBTT) region shows test specimen thickness (TST) effect and temperature dependence, and apparently increases when compressive residual stress is applied. In this paper, as TST effect and temperature dependence, the fact that Jc apparently increases due to compressive residual stress is attributable to the loss in the one-to-one correspondence between J and the crack-tip stress distribution, and then, the fracture prediction of the specimen with compressive residual stress was performed using the T-scaling method proposed by the authors, and its validity was confirmed for high strength steel of 780 MPa class and 0.45 % carbon steel JIS S45C. In addition, it was suggested that the minimum of Jc with compressive residual stress can be predicted by requiring only the tensile test.
In industrial devices such as heat exchangers, fuel cells, and chemical reactors, the fluid flow enters the inlet manifold and streams into many branch passages. In order to improve the performance of these devices, it is important to obtain a uniform flow rate distribution in each passage. In the present study, an experimental investigation is performed for multiple-passage duct flows. The multiple-passage duct is a reverse flow type and consists of five branch ducts. The duct flows are investigated from the view-point of flow uniformity and pressure loss. Experiments are performed for Reynolds numbers ranging from 6.0 × 102 to 1.5 ×103, based on the bulk velocity and hydraulic diameter at the inlet duct. The aspect ratio (i.e., the ratio between the height and width of the branch duct) is varied as 0.6, 1.0, and 20. The effect of the outlet manifold volume on the flow distribution is investigated. The wall static pressure is measured, and the pressure loss and flow rate are evaluated. The velocity profiles are measured by a PIV system in order to clarify the effect of the increasing the outlet manifold volume. The results reveal that the flow rate changes only slightly with the aspect ratio. As the Reynolds number increases, the uniformity of the flow rate through each branch duct worsens. A uniform flow distribution is realized by increasing the volume of the outlet manifold. The flow uniformity is related to the reduction of the recirculation region at the inlet manifold.
For hydrodynamic cavitation produced by a Venturi tube, cavitation bubble is collapsed at downstream of a nozzle and its intensity is influenced by upstream pressure and downstream pressure. In order to investigate the effect of the upstream pressure p1 and the downstream pressure p2 on aggressive intensity of hydrodynamic cavitation, an experiment measuring acoustic power by an AE sensor was conducted. Relationship between pressure conditions and acoustic power PA was studied. The higher the upstream pressure p1, the higher the acoustic power PA. Acoustic power had a maximum value at the upstream pressure p1 = 1.6, 2.1, 2.6, 3.1 and 3.6 MPa. At the upstream pressure p1 = 2.6 MPa and the downstream pressure p2 = 0.5 MPa, the aggressive intensity of hydrodynamic cavitation increased to be 36 times larger of the value corresponding to the atmospheric downstream pressure. While the optimum downstream pressure depended on the upstream pressure, the cavitation number was nearly constant for all upstream pressures. It was concluded that increasing the downstream pressure is an effective means to increase the aggressive intensity of the hydrodynamic cavitation without increasing the input energy.
For the development of industrial heat pump systems supplying high-temperature heat source over 130 °C, experiments were carried out on cooling heat transfer of supercritical pressure HFO1234ze(E) flowing in a plate-type heat exchanger (PHE). HFO1234ze(E) with low Global Warming Potential (GWP) is expected as an alternative to refrigerant HFC134a. In the experiment, heat transfer coefficient data were obtained at different pressures including a near-critical pressure condition. To obtain the heat transfer coefficient, an integral method was used for evaluating the mean temperature difference between the refrigerant and cooling water in the PHE. Based on the measurements, characteristics of cooling heat transfer of supercritical pressure HFO1234ze(E) in the PHE were clarified. Generally, heat transfer coefficient showed considerably large values compared with tube flow, attributed to strong turbulence or agitation promoted by corrugated geometry of the PHE plate, and reached a maximum in the vicinity of the pseudocritical point. As the pressure approached the critical pressure, the peak of heat transfer coefficient became higher at lower bulk enthalpy, reflecting the pressure dependence of isobaric specific heat of the refrigerant. These results mean, even in the pseudocritical region where strong temperature dependency of physical properties appears, properties change in the flow cross section was small compared to the tube flow, although not negligible. The correlation developed in the previous study overestimated the measured heat transfer coefficient in the pseudocritical region for the pressure of the reduced pressure 1.01 very close to the critical pressure and also in the enthalpy region near to and lower than the pseudocritical point for the pressures of the reduced pressure about 1.1 or higher. For the better prediction, the necessity to consider the small but non-negligible properties change in the flow channel cross section was recognized.
Microgravity experiments of flame spread along a fuel droplet array were performed to examine the effect of ambient pressure on the flame spread speed. The purpose of this research is to investigate growth mechanism of group combustion of fuel droplets. A fuel droplet array was suspended by SiC fibers of 14 μm in diameter. The number of fuel droplet was varied from 6 to 10 depending on the droplet spacing. Nondimensional droplet spacing and ambient pressure were varied from 2 to 12.5 and from 0.10 to 0.60 MPa, respectively. To simulate flame spread through a 3D fuel-droplet-matrix, a fuel droplet array was placed on the axis of a rectangular optical cell. n-decane was employed as a fuel. The normalized flame spread speed decreased as the ambient pressure increased. For all ambient pressures, the normalized flame spread speed takes the maximum between 3 and 3.75 in the nondimensional droplet spacing. The dependence of the normalized flame spread speed on ambient pressure increases with the increase in the nondimensional droplet spacing. An empirical model equation which expresses the dependence of flame spread speed on the ambient pressure was proposed.
A range sensor is known as one of sensors which are often installed in mobile robots. The range sensor can detect the distance to objects in the environment using laser beam. However, the measurement area of the range sensor is limited because the scanning plane of the sensor is single and parallel to the mounting surface. In this research, we developed a new range sensor capable of scanning in two directions. Using the periodic refraction of laser beam generated by the rotation of two acrylic prisms installed around the range sensor, two-directional scanning is realized. If this range sensor is placed at the front of the mobile robot horizontally, the robot becomes possible to scan both distant area and road surface. In addition, we devised a simple method for the classification and integration of two-directional measurement data based on a model fitting method. In this paper we describe the concept of the range sensor device and explain the method for the classification and integration of two-directional measurement data. Furthermore, we verified the range sensor's effectiveness through object detection experiments.
Ti-Ni based Shape Memory Alloy (SMA) actuators have been used for robots because of their high power-to-weight ratios, easiness of simple ON-OFF driving, and flexibility. In addition, SMA actuators enable simultaneous self-sensing and displacement control of themselves by feedbacking their electrical-resistance values. Modeling of SMA actuators for servocontrol is not easy due to their characteristics such as nonlinearity, hysteretic behavior, and effect of temperature and stress. Most of past studies have not considered minor-loops in the hysteresis or simultaneous variation of temperature and stress; both are necessary to be considered when achieving a robust robot control with SMA actuators. This study proposes a novel SMA model for electrical-resistance feedback control, which enables to adapt load disturbance and easy implementation. Especially, in order to consider the stress and temperature variation and minor-loops of hysteretic behavior in the relation of temperature and strain, electrical-resistance model and phase transformation models were improved by considering phase transformations between three crystalline structures: austenite, twined-martensite and detwined-martensite. Displacement, stress, temperature and volume function of each phase can be calculated from applied voltage and electrical-resistance value, which are easy to observe. Model parameters were identified by applying several general experiments to the actual system. Through the verification experiments, calculation results of the proposed model from observed electrical-resistance values were confirmed to agree with the experimental results under complex temperature and stress variation. Subsequently, an electrical-resistance feedback control system with the proposed SMA model was developed, and the system showed to control the displacement successfully to a constant value with load disturbance.
A no-backlash drive control technique in which two motors drive a load axis, as one is for a forward direction and another is for a reverseone,hastwo problems :1)the drive system has a remarkable power loss, 2) the 1st natural frequency of the drive system may cause a backlash.For the former problem,weemploy a torque crossover method, in which a part of torque reference of the drive-side motor gives to the driven-side motor and the resulted torque reference of the driven-side one is reduced.For the latter problem,we employ a ratedifference feedback method that feedbacks a signal in proportion to the difference between the forward direction motorvelocity and the reverse one to the each motor torque.We have shown through our analysis thatthetorquecrossover does not affect poles of the 1st natural frequency, andthat theratedifference feedbackimproves the damping of the 1st natural frequency directly and suppress its vibration.We evaluate our method in the non-linear simulation andexperiment:1) it is preferable to increase the damping of the1st natural frequency with theratedifference feedback and then decrease the motor current with theratedifference in the control system tuning, 2) the torque difference between the two motors is required to some extent for no-backlash drive, so torque crossover should not be increased unnecessarily.We have gotten the experimental results that the total motor current has been reduced by 40%.
In the steel/casting industries, a liquid container transport is carried out by an overhead traveling crane or a trolley. The operation of the overhead traveling crane is carried out both operation by the experience operator and operation by automated transportation in order to prevent quality deterioration due to the overflow and involvement in a hostile environment. In particular, the overhead crane transportation by the operator, which is allowed to select freely pathway, is needed from the point of freedoms of the operation. This paper presents a design of a liquid container transport control system with an overhead traveling crane, which is allowed to operate by an inexperienced operator easily. The presented control system is designed as to suppress both the rod vibration and the sloshing (liquid vibration) without measuring the sloshing. The presented control system is two DOFs controller, the feed-forward controller is based on two notch filter, and the feedback controller is based on the H2/H∞ controller design method using LMI. The derived controller is performed a controller order reduction in consideration with practical use. Some experiments are presented to show the effectiveness of the proposed design of control system.
A long flexible shaft such as a lance tube in a soot blower or a drill string in a rotary drilling system exhibits friction-induced vibration resulting in a whirling motion. This paper investigates the whirling motion of a long flexible shaft induced by frictional force and examines the effect of an intermediate support position on the whirling motion. The experimental apparatus investigated has a vertical shaft which rotates at a constant speed by means of an electric motor mounted at the top of the shaft. At the bottom end of the shaft is located a rubber ring so that frictional force acts on the tip of the shaft when the shaft is deflected. Comparing experimental and calculated results we clarify the vibration characteristics, such as whirling frequencies and amplitudes, at various rotational speeds and show the effective position of an intermediate support to suppress shaft vibration.
In minimally invasive surgery robots, force sensing is required to improve its manipulability. To perform delicate surgery, three-axis force sensing is desired. However, in general, the force resolution in the axial direction is worse than that in the radial direction owning to a slender shape of a forceps. This paper proposes a double diaphragm structure for forceps flexural elements. The distance between the two diaphragms can adjust the rigidity in the radial direction without changing the rigidity in the axial direction when the thickness of the diaphragm is constant. Thus, the thickness of the diaphragm adjusts the rigidity in the axial direction, while the distance between the two diaphragms adjusts the rigidity in the radial direction. A planar spiral cutting in the cross section of the diaphragm can reduce the maximum stress applied on it. Moreover, by adjusting the two spiral phases and direction, the crosstalk of the radial and axial forces can be reduced. In 5 mm forceps simulation, the rigidity of the axial direction is almost equal to that of the radial direction when the distance between the two diaphragms is 6.0 mm. We performed experiments of 10 mm forceps model and confirmed that the resolution of the radial direction is almost equal to that of the axial direction when the distance between the two diaphragms is 12.0 mm.
Vibration testing using a shaking table is a useful method to examine the vibration characteristics such as aseismic capacity of buildings for earthquakes and ride comfort of vehicles for vertical vibration. However, it’s necessary to design a controller which can reproduce the vibration such as earthquake waves accurately. Moreover, since there are various types of earthquakes such as a long-period earthquake and short-period earthquake, a controller with good tracking performance on wide frequency range is required in order to reproduce earthquake waves. Generally, a displacement feedback controller is employed in a control of the shaking table. However, almost all earthquake waves are saved as acceleration data. Therefore, an acceleration feedback controller is more proper to control the shaking table. The purpose of this study is to design an acceleration feedback control system with good tracking performance until high frequency range. However, it generates spillover caused by dynamics that is not included in plant model. As a result, the tracking performance of the controller degrades. So, we also proposed the method which can suppress spillover to solve this problem. The controller is designed based on Dual Model Matching method. Then, effectiveness of proposed control system is validated by experiments using 3degree-of-freedom shaking table.
Horizontal moving body settling control mechanism which is mainly realized by momentum exchange, can be expected to save time of article transportation. Momentum exchange impact damper (MEID) is one of the mechanisms in order to solve shock response control problems. This paper proposes a novel hybrid mechanism consisting of passive MEID (PMEID) deceleration and active MEID (AMEID) rebound suppression for realizing rebound reduction of horizontal moving body colliding with a wall. In this method, all of the dampers are not released to the outside of the horizontal moving body but captured by soft springs to assume the actual usage condition. For the same reasons, the function to reduce the rebound and to extend the time in the state of zero rebound velocity is especially focused. The effectiveness of the proposed method is discussed by simulations and experiments. Simulations are conducted with both ideal and experimental conditions. Compared with the system with AMEID or PMEID only, the proposed hybrid MEID combines the advantages of each system and can realize settling control efficiently without releasing dampers out of the horizontal moving body. Ideal simulation results show that it is possible to reduce the rebound and the acceleration of moving body at the time of the collision, and reduce the active control input, simultaneously. These two advantages of the proposed method are also shown by the simulations with experimental conditions and the experimental results.
Acoustic metamaterial can have arbitrary acoustic characteristics , and there is possibility to improve acoustic performance of any products dramatically. As metamaterial, many kind of types have been propounded and studied. It is mainly classified into resonance type and non-resonance type.Resonance type metamaterial can change acousic characteristics drastically, but frequency range is narrow. Non-resonance type’s acoustic characteristics range is less than resonance type, but it can be changed in broad frequency band. It is a great advantage to use. About non-resonance type metamaterial, it has been already studied to control transmitted sound, but it has not been studied about reflection sound. If reflection sound control become possible, effective method can be chosen to solve noise problem. For example, resonance frequency in a duct will be shifted by changing reflection direction from the wall. In this study, the design method of non-resonance type metamaterial to control reflection sound has been studied by using FEM and Transfer-function method, and to verify the design method, element test was conducted. Element test result correspond well with analysis result, and the design method of acoustic metamaterial has been verified in this study. In order to put into practical use, further study with actual product shape is needed to confirm manufacturability.
Response distribution of a SDOF linear system subjected to non-Gaussian random excitation is investigated. The excitation is modeled by a zero-mean stationary stochastic process prescribed by the non-Gaussian probability density and the power spectrum with bandwidth and dominant frequency parameters. In this paper, we use bimodal and Laplace distributions for the non-Gaussian distribution of the excitation. The excitation is generated numerically by using the Ito stochastic differential equation. Monte Carlo simulations are carried out to obtain the stationary probability densities^ of the system displacement and velocity. It is found that the shape of the response distribution changes depending on a difference in the shape of power spectral density between the excitation and the response. In order to evaluate the difference of the spectral densities quantitatively, a new index is defined. The correspondence of this index to the shape of the response distribution is shown. Next, we compare the present difference index of power spectra and another index which the authors used in the previous study to investigate the response distribution of a non-Gaussian randomly excited system. The comparison shows that when the present index is close to 0, the shape of the response distribution looks like the shape of the excitation distribution. For the index around 0.6, the response distribution becomes the middle shape between the excitation probability density and a Gaussian distribution. In the case of the index greater than 1.2, the response distribution is nearly Gaussian. The difference index of power spectra between the excitation and the response can be calculated readily from the frequency response function of a linear system and the excitation power spectrum, regardless of the excitation probability density function. This index enables us to roughly estimate the shapes of the probability distributions of the displacement and velocity responses without Monte Carlo simulation.
In order to clarify the mechanism of the vehicle body hysteresis affecting “rigidity feeling”, one of the driver's sensory evaluation in the driving test, the influence of friction acting on spot welding flanges on hysteresis, which is drawn by displacement - load diagram under static or relatively slow deformation of double-hat-shaped parts assembled by spot welding, is experimentally evaluated. By measuring the difference between loss energy of a specimen with strong contact on welding flanges and that of another specimen without contact, friction loss (energy dissipation generated only by friction excluding inevitable loss energy for measurement possessed by testing system itself) is calculated. The friction loss rising with increasing load amplitude and load rate confirms that friction hysteresis occurs in the structure even under the elastic deformation. In this paper, the load rate dependence and the extrapolation point to the zero load rate are evaluated as the dynamic and static characteristics of friction loss, respectively. As a result, the dynamic characteristic obtains a result proportional to the load amplitude, and the static characteristic is proportional to the square of the load amplitude. Additionally, a model with the reaction force as the sum of linear elastic resistance due to bending and shear deformation, Coulomb friction proportional to amplitude of displacement and viscous friction is proposed. Using this model, the prediction of static and dynamic characteristic of the friction loss shows good agreement with results of the experiment. Finally, the friction-induced hysteresis led from the model is quantitatively discussed.
This paper presents numerical solution to two shape design problems of unsteady forced heat-convection fields to control temperature to a prescribed distribution. In the first problem, the square error integral between the actual temperature distributions and the prescribed temperature distributions on the prescribed sub-domains during the specified period of time is used as the objective functional. In the second problem, a multi-objective shape optimization problem using normalized objective functional is formulated for the temperature distribution prescribed problem and the total dissipated energy minimization problem in the unsteady forced heat-convection fields. Shape gradient of these shape design problems is derived theoretically using the Lagrange multiplier method, adjoint variable method, and the formulae of the material derivative. Reshaping is carried out by the traction method proposed as an approach to solving shape optimization problems. Numerical analyses program for the shape design is developed based on FreeFem++, and the validity of proposed method is confirmed by results of 2D numerical analyses.
Structure can get various mechanical characteristics by applying periodic structures as typified by lattice structures. Lattice structures are generally used inside the structural member in order to reduce the weight. One advantage of lattice structures is that we do not need to change the whole structural shape when we replace the solid part of a component with the lattice structures. Another advantage is the lightness of the weight, and hence it is important to design a high performance lattice shape with low weight. However, a framework for development of micro lattice structures considering both stiffness and weight has not been established. Thus, we propose a method for designing and producing micro lattice structures. We use a topology optimization method for a designing methodology. Topology optimization is an effective method in designing high performance lattice structure since topology optimization allows us to change the topology and to design a complicated shape. We use a metal additive manufacturing (AM) machine for producing the optimal lattice structures. AM allows us to produce a complicated structure which removal and forming manufacturing cannot produce. We use a bulk modulus as the objective function since it is one of the important mechanical characteristics in design. In this research, we use a homogenization method to compute the bulk modulus. Objective function was modified so that isotropy of the optimal shape is retained when the solution is updated. In addition, structures produced by AM need holes so that internal metal powder can be removed. Hence, we defined the design domain so that the optimal structure becomes open cell structure. Then, high bulk modulus shapes were derived using topology optimization. The lattice structures were produced by metal AM machine after being modified for production.
The purpose of this study is to construct the automation technology based on the hammering task and its sound feedback with an industrial humanoid robot equipped with an integrated system of vision, sound and dual arm motion. First, we discuss a suitable flexible rubber stick to achieve the hammering task and developed the acoustic recognition system based on its hit sounds. Second, we confirm that the developed system is sufficient to investigate the task playing the glockenspiel, and also discuss the characteristics of motion based on dual arm motion. Third, we attempt to cooperate with hammering the bottle and pouring liquid into it based on estimating its hit sound. As a result, it can be seen that the proposed system using an industrial humanoid robot achieves sufficient motion accuracy. Therefore it is demonstrated that the proposed approach is found to be effective to construct the automation technology based on the hammering task and its sound feedback with an industrial humanoid robot.
In recent years, the drill used to make holes is expected to exert both high machining accuracy and good processing capability. In order to meet those requirements, it is necessary to develop a new drill shape with good properties requested by designers. There is a strong need for a new system to shorten the drill fabrication time, to reduce material costs, and to create new drill configurations by predicting their characteristics. Current drill shape prediction systems cannot comprehensively and mathematically treat drill cross-section shape including the cutting edge, groove and so on. The prediction system would become more practical if the drill specification was mathematically formulated. This study reports the development of a system to predict not only the cross-sectional shape but also various parameters from the information of grinding wheels used in drill fabrication. Furthermore, this study proposes the new system to predict the most suitable grinding wheel setting from the grinding wheel shape and some drill specifications as the reverse process.
Recently, a titanium alloy has been as biomaterials that have stable mechanical property and superior biocompatibility. But the titanium alloy generally has higher young’s modulus in comparison with cortical bone, then bone resorption was occurred by stress shielding. For this reason β-type titanium alloy exhibiting super-elasticity and super-plasticity was developed. This alloy has high tensile stress and low young’s modulus too. However, the characteristics of this alloy is lost by severe heat environment and external force. Therefore, there is possibility that the advantageous characteristics may be lost during cutting. In this study, the effect of cutting temperature and cutting force on the affected layer was investigated by milling with small ball end mill tool in order to decrease the affected layer by cutting process. At the cutting speed of 16.0m/s, the thickness of the affected layer exceeded 2.5μm because of increasing of cutting temperature that approached to the neighborhood of transition temperature of this alloy. On the other hand, the affected layer was observed for the cutting condition of high cutting force by increasing feed rate of a tooth, depth of cut and pick feed, the thickness of the affected layer was 0.7μm .So, the affected layer was dominant by the influence of cutting temperature. To decreasing affected layer, the cutting temperature is able to decrease to decreasing feed rate of a tooth or depth of cut.
This paper describes that the film formation and shear properties of screw tightening lubricant PIB (Polyisobutylene) under the oil starvation condition. The point contacted pure sliding tests were conducted, and the film thickness was measured using the interferometry method with the spacer layer. The result showed that the starvation region occurred at the inlet of the conjunction becomes large with time. It was also shown in the initial time of the test that the film thickness decreases due to the oil starvation, however, the thickness is thicker than the value equivalent to surface roughness. The friction coefficient depended on the starved area, and that showed the constant value of 0.16-0.17 in the fully starved condition. The relationship between the friction coefficient and the shear rate suggested that the coefficient in the high shear rate condition is the constant value, that revealed the film may be changed to the solid like film with the high shear strength in the fully starved condition. The long term test showed that the breakdown of film is appeared at about 120 s and then the wear area expands in the remainder of the test. The test results suggested that the PIB lubrication film has the high shear strength and enable to protect the contact surface in the tightening screw from the direct contact and the wear.
Multi-fidelity analysis has been used for reducing the calculation cost of evaluating the design solution, which is the most costly process in design optimization. In general, multi-fidelity analysis is applied to problems with continuous design variables, which are suitable to construct an approximate model of design space such as the response surface. On the other hand, combinatorial optimization problems, e.g., layout design, are difficult to apply the conventional multi-fidelity analysis, since the response surface cannot be constructed due to the property of the design variables. In this paper, we propose a multi-fidelity optimization method independent of the response surface and a simple analysis model for the method, and apply them to multi-disciplinary optimal layout design problem which is a complicated combinatorial optimization problem. The proposed analytical model, which adopts the concept of the explicit method, realizes for reducing the calculation time by simplifying the physical phenomenon. Then, the multi-fidelity optimization method is constructed by combining the proposed analysis model with the thermal network method which is a well-known thermal analysis method. We confirm that there is a strong correlation between the calculation result of the proposed analysis model and of a CAE software, and show that the proposed analysis model is suitable as a low fidelity model. The effectiveness of the proposed optimization method is demonstrated through numerical experiments.