Sensing the state of structures, such as automobiles, factory machines, and buildings, is essential for structural health monitoring and structural vibration control. Strain, displacement, and acceleration sensors can measure the structural information; however, these sensors require certain installation spaces, wiring between sensors and data loggers, and electricity for data recording. To solve these technical subjects associated with the sensor installation, we have proposed a self-sensing technique with a stand-alone harvester. The technique estimates the structural information from piezoelectric voltage generated from a piezoelectric transducer inserted in a target structure. Because the piezoelectric voltage is proportional to the mechanical displacement and the electric charge, the proposed observer can estimate both electrical and mechanical information from the harvester. The transducer acts as two roles: a sensor utilized for self-sensing technique and an energy scavenger converting mechanical vibration energy to electrical energy. The scavenged electrical energy is applied to sense the piezoelectric voltage, which is calculated to estimate the structural displacement and velocity from the sensed voltage information. To achieve this objective, an alternately switching observer based on the Kalman filter theory has been introduced. The scavenging performance is enhanced by an appropriate mechanism for circuit connection changing. This paper reports the estimation performance of the proposed self-sensing method through an experiment under a noisy observation value condition. This consideration supposes real-environment operation. The estimation performance of the self-sensing method was evaluated by indirectly determining the harvesting performance. The experimental results showed that the proposed method can accurately estimate the state values under noise-contaminated conditions.

Next-generation aerospace structures, such as deployable wing aircraft, consist of very flexible bodies connected by joints because they are required to be lightweight. In designing the structures, a deployment simulation considering the high flexibility and joint is necessary. Multibody dynamics with absolute nodal coordinate formulation (ANCF) is effective for the simulation. ANCF is a nonlinear finite element method that can easily describe flexible deformation and constraint joint equations. However, ANCF cannot be easily applied to complicated cross-sectional structures such as a wing. This is because the volume integral necessary for the elastic force derivation is difficult for complicated structural shapes. To solve this problem, we present an ANCF beam element with internal constraint equations (ICE). ICE restricts the non-dominant deformation. Consequently, a line integral can be used instead of the volume integral. We demonstrate that the ANCF-ICE beam element can describe the very flexible deformation of a complicated cross-sectional structure in a flying wing simulation.

One of the authors had presented a novel seismic sensor using feedback control to extend the measurable frequency range to such lower frequency. An ordinary seismic sensor utilizes a mass-spring-damper system possessing lower natural frequency so that relative motion of the mass over the natural frequency domain can be measured as absolute motion of the ground. Therefore, if the natural frequency is lower, the measurable range of the seismic sensor is wider. To realize lower natural frequency, one of the authors introduced feedback controller and output shaping. According to this idea, as low as 0.1 Hz of ground motion can be measured. However, a digital feedback controller using classical control theory in the previous study had problems such as limitation of measurement range, and mismatch of the measurement signal in large amplitude vibration. In order to improve measurement performance, we aim to introduce the controller with modern control theory. This control theory can obtain more accurate measurement signal because it can utilize state variables. To measure the relative displacement of the sensor in order to do modern control with two state variables, one of the authors introduced a photo reflector in a previous study. In this study, the authors designed a controller based on modern control theory and simulated the sensor using MATLAB when applying the control. We also applied this controller to the sensor and did an experiment to confirm its performance. From these results, the performances of simulation and experiment were confirmed good agreement. Therefore, it was confirmed that the sensor could be controlled by the controller using modern control theory.

Piezoelectric vibration energy harvester should harvest electricity from kinetic energy effectively. The passive harvester is limited in its harvesting performance by the scale of the disturbances. Intellectual harvesting has been proposed to obtain higher harvesting performance than the passive one from the same scale of disturbance. The intellectual harvesting is realized by a voltage inversion circuit, a specific control strategy, and a controller, which has enough computational capacity to achieve the adopted control strategy appropriately. The initial intellectual harvesting has been implemented by an analog controller, which has low energy consumption but low computational capacity, and a simple strategy. For higher performance and wider usage than the initial strategies, the computational capacity of the controller has required to increase in proportion to the complexity of the recent strategies. We proposed the stand-alone active harvester equipped with the digital controller to accomplish a novel control strategy for complex but high performance. The stand-alone harvester is driven in self-powered by the harvested electricity itself without an external energy source. The harvester has the noise reduction function with an observer based on Kalman filter theory owing to its high computational capacity and achieves appropriate controlling following the strategy even if noise is contaminated in an observation value. This study shows the whole evaluation of the proposed harvester.

In general, a stacker crane in a large automatic warehouse is heavy. The weight reduction of large stacker cranes greatly contributes to the improvement of warehouse system capacity. In order to greatly reduce the weight, we devise a suspension crane with a traveling drive unit on top of the stacker crane. By using a hanging pin structure and Adopting a linear motor. On the other hand, the suspension pin structure is greatly shaken, and the linear motor has a large friction. As a result, the required propulsive force may not be obtained with respect to the commanded current, and positioning as a crane becomes difficult, and the load cannot be transferred to the rack due to shaking, which adversely affects the tact time. In this study, we will use a physical model that captures the characteristics of a suspended crane to realize traveling control that does not excite the crane swing. Specifically, a two-degree-of-freedom (2DOF) control that follows the reference model is constructed, and feed-forward input and position reference that do not excite shaking are given. In order to reduce the influence of large friction, the Kalman filter is used to estimate the external force and the speed and position of the drive unit, and to control the movement and vibration of the suspended crane. Its effectiveness is verified by simulation and experiment.

The conventional researches on energy harvesting based on stochastic resonance use bistable vibration systems, Normally, the energy harvesting efficiency will be improved when vibrational amplitude increases. However, most conventional researches are use cantilever which is small-scale and difficult to apply into practice use. Therefore, how to develop a compact large-scale device becomes a key problem for vibrational energy harvesting. This study firstly proposes a horizontal large-scale bistable model to increase vibrational amplitude to improve robust performance of disturbance force, relative to conventional bistable vibration systems. Furthermore, an experimental device is fabricated to realize stochastic resonance phenomenon, and its bistable vibration performance is carefully investigated with the excitation of random and periodic signals. At last, we use standard deviation to evaluate increase rate of this horizontal large-scale bistable model.

HOPG (Highly Oriented Pyrolytic Graphite) means highly oriented graphite. The diamagnetic current that flows through the hexagonal mesh surface of the carbon that constitutes it causes the HOPG diamagnetism. The diamagnetic force changes depending on the direction of the outer magnetic field and the direction of the hexagonal mesh surface of carbon. We show that the combination of cylindrical HOPG and HOPG disk can increase the diamagnetic force in the axial direction of the HOPG disk.

Mitigating unwanted vibration in civil engineering structures is an important part of the design process, particularly for structures that may be subject to seismic excitation. This paper introduces a passive control device based on the conventional tuned inerter damper (TID) designed for the passive control of seismically excited multi-degree of freedom (MDOF) building structures. The proposed system is based on the conventional TID, with the main difference that its location is changed from the ground level to the last two story-levels of the structural system. Besides, this study employs a metaheuristic optimization based on the differential evolution method (DEM) combined with an elastic displacement history analysis in the time domain, through which the vibration control focuses on two individual objectives: first, minimizing the horizontal peak displacement; and second, minimizing the root mean square (RMS) response of displacement. A case-study of a 12-story building equipped with the novel TID scheme is subjected to seismic base excitations represented by four accelerograms of recorder earthquakes in order to verify the TID effectiveness. The results show a significant enhancement in the dynamic response when the TID arrangement proposed herein is applied, better than an equivalent TMD. Therefore, this proposal represents a potentially attractive alternative to traditional passive control techniques.

The present paper investigates the vibration characteristics of CFRPs including the anisotropic damping properties. Carbon fiber (CF) preforms are prepared by a tailored fiber placement (TFP) machine, and the electrodeposition resin molding (ERM) method is used to impregnate the resin into CF preforms. CFRP plates are fabricated by two different methods which are the ERM and vacuumed assisted resin transfer molding (VaRTM), and experimental modal analysis is conducted to compare the vibration characteristics of those plates. The experimental results show plates fabricated by the ERM exhibit higher damping properties than those by VaRTM. Then, anisotropic damping properties of the present CFRP plates composed of plain weave layers and TFP layers are identified using the finite element analysis (FEA) with the experimental results. In this analysis, the damping properties are modeled by specific damping capacity (SDC) that is defined as the ratio of the dissipated energy and the maximum strain energy in one cycle of loading. Those parameters are determined by minimizing the difference between modal SDCs calculated by the FEA and measured by the experiment. To solve the minimization problem, particle swarm optimization (PSO) is used. Obtained damping parameters enable us to design damping properties more flexibly for CFRPs with arbitrarily shaped fibers.

In this paper, we propose a novel control method that incorporates model predictive control (MPC) and semi-active control. Semi-active vibration control is excellent in damping effect, energy consumption, and system stability. With the degree extension of the MDOF system, parameter tuning might be complicated in the conventional semi-active methods. Therefore, in order to extend the diversity of the input decisions, MPC and semi-active control are integrated. MPC can design control input trajectories arbitrary. A predictive controller has an internal model and predict future states of a system among a prediction horizon. The future states are optimized by selecting the most desirable input trajectory. Future states of a system are predicted based on two assumptions. The first assumption considers future control inputs are expressed as summations of harmonic functions. The second considers that periodic disturbances that cause resonance are applied to a structure. Switching is conducted to match the polarity of the charge of the piezoelectric transducer with target inputs derived based on the proposed method. Switching based on the prediction can achieve more effective vibration suppression and easier tuning than conventional semi-active methods. Computational loads are reduced by appropriately designing input trajectory. The beneficial features of the proposed method are demonstrated in simulations and experiments.

The research concentrates on evaluating the impact of phase fluctuation and distant effect between two antennas in our developing "smart gear health monitoring system" using directly printed crack detection sensors on gear technique. Due to the importance of the magnetic resonant signal occurring when these two antennas are paired to the crack detection quality of our technology, the consideration of these effects, hence, is essential. The study has employed both theoretical simulation and experimental work for validation of the results. For simulation result, a Multiphysics simulation environment, namely COMSOL Multiphysics version 5.4 is used for evaluation while for experimental results, a developed laser sintering technology of conductive ink (NPS-J Harima) is utilized to print a pattern of designed open spiral antenna on polyacetal (POM) plates with polyimide layers covered on their surfaces. In the case of the phase fluctuation consideration, the relative phase angle of two antennas is selected from 0 to 360 degrees with an increment of 15 degrees and in case of distant effect, the relative distance is selected in the range of 0 mm to 4.9 mm with increment of 0.1 mm. By scrutinizing and comparing the achieved results, it shows that the experimental results approximately agree with the simulation results. Consequently, the phase fluctuation and relative distance have undoubtedly influenced to the physical electromagnetic resonant coupling formed between this smart gear antenna and its monitoring antenna. Since the phase fluctuation will always occur when two rotating antennas are placed in parallel, closely and concentrically, these recognitions certainly play an essential role in the accuracy of our frequency analysis procedure for parameter identification of the system in the near future.

Chatter vibration may occur due to grinding, which may affect product quality and the life of tools and machine tools. There are two causes of these chatter vibrations: forced vibration and self-excited vibration. Above all, the mechanism of self-excited vibration is complicated, and it is necessary to suppress or solve them. In order to solve these self-excited vibration problems, research on cylindrical plunge grinding was conducted. In this study, focused on the rotational movement of the work-piece, which is a characteristic of cylindrical grinding. In addition, a new equation of motion was examined by considering the relationship between the tangential direction grinding force and the normal direction grinding force in cylindrical grinding as the friction phenomenon between the grinding wheel and the work-piece. Based on these equations of motion, eigenvalue analysis was performed using the numerical analysis software MATLAB. The object of analysis was cylindrical plunge grinding of a carbon steel round bar for machine structure having a diameter of 30 mm and a length of 175 mm. As a result, it was confirmed that the analytical model of this study occurs instability, which is considered to be self-excited vibration. This instability is affected by the distance between the contact point of the grinding wheel and the work-piece, which is determined by the grinding conditions, and the center of gravity of the work-piece. In addition, confirmed that increasing the support stiffness of the work-piece can suppress instability. So will report the results.

The external noise is a problem closely related to modern society. There are two ways of noise control methods. One is passive noise control that uses absorbing or insulating materials. The other is active noise control that generates the sound of the opposite phase with the noise by the secondary speakers. Since the effective frequency band of the noise reduction in each method is different, using both methods has been researched to expand the controllable frequency band for dealing with various noise. In order to apply active noise control, the information over the control region is required to obtain a control filter of control speaker. However, the general method that arranges the microphones over the control region can be the obstacles to the user, therefore the other method is needed to obtain the control filter. One way to obtain the control filter without the arrangement of the microphones is using the theoretical model and the control filter can be obtained relatively easily based on the theoretical model. Therefore, the theoretical model is generally used to estimate the maximum performance by simulation. However, there is less research for studying the applicability of the ANC system with a finite noise barrier based on the theoretical model and the verification of the control filter is required by investigating noise reduction performance in the experiment. In this paper, the control filter is obtained based on the theoretical model and noise reduction performance is investigated in the experiment for verification of the control filter.

The standing movements of elderly people and people with motor disabilities are generally associated with a high risk of falling. We measured and analyzed the angle of the human lower-limb joints during standing motion using an optical motion tracking system. From the results, we found that there is a coordination mechanism between the lower-limb joints. Moreover, we retrieved that the movement mode of standing up motion can be categorized into two types, which are "switching" rather than "transition."

Accurate assessment of the balance during standing is one of the important issues for the prevention of falls and detection of diseases. Although there are a lot of methods for assessing balance, this study aims to obtain a model of individual balance by system identification based on the white box modeling. The target for the assessment is a steady balance response to horizontal oscillation of the support surface on sagittal plane. There are two problems to achieve the identification. The first problem is to define a simple model reproducing the response. In order to reproduce the response below 0.2Hz, we introduced a cascade control system and defined the reference displacement of the center of mass of the body according to velocity of the support surface as the outer-loop system. The second problem is to simplify the measurement of the center of mass of the body for practical use. We proposed a method for estimating the center of mass of the body from force plate measurements, and verified its accuracy by comparing it with the measurements of the three-dimensional motion analysis system. As a result of experiments with three subject, we found that the parameter identification of the proposed model can be achieved based on the force plate measurements.

Failure detection of gears in transmissions plays a critical role in the development of machinery health monitoring system. Although many studies of metal gears health monitoring have been carried out, plastic gear failure detection has been mostly unknown. To perform more research projects on plastic gears, we constructed an automatic data acquisition system in our laboratory. Many endurance tests were carried out from healthy until broken situations to collect vibration data of plastic gears. In the endurance test, the crack growth of gear tooth root can be captured by a high-speed camera, which then was used to label data. Besides, an intelligent diagnosis system was developed to monitor the condition of plastic gear during the endurance test. The proposed system can learn from visualized images created from vibration data. In orient toward achieving high accuracy of learning by the proposed system, an enhanced method was discovered to collect valuable information into data. In this paper, the Fourier decomposition method was employed to reconstruct data from some specific frequency bands. The evaluation of reconstructed data not only revealed an unhealthy situation of plastic gear before initial crack happened but also indicated sensitive frequency bands that can be used for efficient learning.

Acoustic Black Hole (ABH) structures with the functions of wave manipulation and energy focalization have potential applications in broadband structural vibration suppression. In this study, the vibration transmission characteristic of a plate strip embedded with different placements of two-dimensional (2D) ABHs was investigated. The simulation results show that the width and intensity of the attenuation bands with low vibration transmission depend on the number of 2D ABH and the spatial distribution. The numerical investigation method was utilized to understand the mechanism of the attenuation band generation. The analysis concludes that the modal displacement cancellation in symmetrical structures dominates the formation of attenuation band. The strong local resonance in ABH areas plays an important role in generating more than one pairs of modes to achieve modal displacement cancellation. The attenuation phenomenon in ABH-plates with variable spacing between adjacent ABH cells reveals the transition of attenuation band. Analyses on the modal response, phase and vibration characteristic show that the spacing influences the mutual-interactions among ABH cells, which exhibits as the transition of local resonance behavior in ABH cell. These results enrich the existing knowledge on ABH-induced vibration attenuation characteristic. It is hoped that the present work can offer a design guideline of ‘bandgap-like’ behaviors in an ABH plate.

In this paper, the performance of semi-active vibration suppression by a shear-type MR grease damper is experimentally investigated. The shear-type damper using magnetorheological grease (shear-type MR grease damper) is one of MR dampers that are widely studied as promising devices for semi-active vibration suppression. It was developed to overcome the two issues in conventional pressure-type MR fluid dampers; the low dispersion stability and the low dynamic range were solved by applying MR grease and shear-type damper, respectively. The high dynamic range would contribute to the high performance of semi-active vibration suppression since it varies the damping properties significantly according to the vibration state. To suppress vibration with a semi-actively controlled current, it is necessary to propose a control strategy that takes full advantage of the high dynamic range. In this study, in order to achieve the high suppression performance over a wide frequency range, a control law called skyhook-based control is proposed to reduce the vibration response not only around the natural frequency but also in the high-frequency range. The results of the vibration suppression test using a small model structure show that the proposed skyhook-based control can reduce the vibration response most successfully of all the methods including the OFF-state, the ON-state, and the conventional semi-active controls such as the ON-OFF control and the conventional skyhook-based control.

In most motion control problems, precise settling in terminal time of control is a crucial specification. Totani and Nishimura, thus proposed the final-state control (FSC) technique which satisfies the required final-state conditions precisely. FSC has been applied to positioning control problems of hard disk drives and other servo systems. Moreover, the authors proposed a real-time updating version of FSC (updating final-state control: UFSC) by taking the application to time-varying final-state conditions into account. UFSC is also one of the promising solutions to many motion control problems. However, huge control inputs often occur at the final control time to suppress the error between the final-state conditions and real state variables, making it challenging to apply UFSC to practical problems. This paper discusses three improved control methods taking the input constraints at the final control time into account to improve feasibility. These are (i) frequency-shaping method (FSM), (ii) time-varying weighting method (TVWM), and (iii) input freezing method (IFM). The effectiveness of the methods has been discussed by comparing the numerical simulation results of a case study. The case study is a mid-air retrieval problem of low-speed-descent objects using fixed-wing unmanned aerial vehicles, which is also discussed in the authors’ prior study. As a result, this paper concludes the IFM based UFSC is the most realistic method for the control problem.

The article presents the conception of a foil bearing control system, in which a feedback loop is used. The purpose of this system is to improve the dynamic properties of the active foil bearing by changing its geometry. In the system presented, the change in the geometry relates to the size of the lubrication gap and the bearing foils. The system consists of a shaft driven by an electro spindle and radial foil bearings with variable geometry. The system whose main task is to optimise the dynamic properties of a bearing consists of three integrated subsystems. The first subsystem is used to measure the position of the bearing and consists of displacement sensors which are arranged in pairs, perpendicularly to the rotor axis. This arrangement of the sensors makes it possible to determine the displacements of the bearing bush in two directions perpendicular to each other. This subsystem also enables signal processing, which allows to calculate the maximum vibration amplitude (based on measured displacements) in two mutually perpendicular directions. A properly processed signal is analysed by the control subsystem to determine the displacements of the bearing components, which can ensure the change of the dynamic properties of the rotor-bearing system during operation. At the initial stage of the research, it was assumed that the control system would be implemented through the appropriate type of controller. The change of the bearing bush is carried out by the executive subsystem that uses actuators. The changes introduced indirectly, by changing the dynamic properties of the gas film and the supporting foils of the foil bearing, make it possible, among other things, to reduce the vibration level and eliminate resonance vibrations.

This study concerns the detection method of contact-type failure based on frequency down-conversion of elastic vibrations. Frequency down-conversion is the phenomenon caused by contact acoustic nonlinearity (CAN) caused by large amplitude ultrasonic vibrations. The contact condition is fluctuated by large amplitude ultrasonic vibration. In this condition, the scatter characteristic of another ultrasonic vibration, of which frequency is close to the large amplitude ultrasonic vibration, fluctuates. As this result, the low-frequency vibration, of which frequency is the difference frequency between two ultrasonic vibrations, generates. The detection method of the contact-type failure based on frequency down-conversion of elastic vibrations is useful to detect small failure. In this study, the novel detection and localization method by measurement of structural intensity of low-frequency vibration is proposed. Frequency down-conversion generates, only when the object has a contact-type failure. Therefore, the contact-type failure can be regarded as an exciting source of low-frequency vibration. The localization of contact-type failure realizes by the measurement of structural intensity of low-frequency vibration caused by frequency down-conversion as a detection method of exciting point. In this paper, the basic investigation of the proposed method is done by experiment using simple cantilever. Firstly, the vibration mode of low-frequency vibration caused by frequency down-conversion is measured. It is shown that the estimation of a failure location from vibration mode shape is difficult. Secondly, the concept of the proposed method is introduced. The structural intensity of the low-frequency vibration is calculated using the measured vibration mode. It is shown that the detection and localization of the contact-type failure can be realized by the measurement of the structural intensity. Finally, the basic investigation of the proposed method is done by experiment. It is confirmed that the sign of the structural intensity of low-frequency vibration caused by frequency down-conversion changed at the failure location.

Space robotic arms should possess lightweight, high rigidity, and compact. To achieve this, we focused on honeycomb sandwich structure. The honeycomb sandwich structure is already put into practical use as plate, while its strength properties in rod shape have not been investigated precisely. In our project, the strength properties of honeycomb sandwich structure in rod shape have been explored. In the previous research, the experimental piece was made by glued FRP plates and aluminum honeycomb core and exfoliation persisted throughout experiment. To overcome this problem, we introduced a 3D printer and shaped the experimental piece integrally. A test piece model is created on 3d CAD software “Creo” to apply theoretical calculation by using finite element analysis (FEM) software “Creo simulate” and to form experimental piece by using a 3D printer “MakerBot Replicator +.” Bending stiffness and torsional rigidity are evaluated through theoretical and experimental analysis. For comparison, the benchmark is SRMS (round pipe shape), and the comparison is made based on the stiffness per unit weight (specific stiffness). A finite element analysis was performed and the honeycomb structure and SRMS were compared. The torsion test and the bending test were performed three times and averaged. The results of the bending test and the torsion test of the honeycomb structure were compared with the analysis results. Theoretical analysis shows that the robot arm using the honeycomb sandwich structure has some advantages over the conventional round pipe type arm. Moreover, the ratio of the experimental value to the analytical value is stable by the integral shaping, although it is about 0.5, and it is thought that the actual rigidity can be predicted to some extent from the analytical value in the future. According to these results, validity of honeycomb sandwich structure for robotic arm is confirmed.

This research presents the implementation of the flexible dynamics model of a mobile crane structure in spatial coordinates that could simulate the motion using a short calculation time. The mobile crane model is consisted of the components with the assumptions of the rigid bodies, a flexible body, a point mass. The model of the flexible body is considered with the floating frame of reference formulation. In this work, the problems of the numerical stiffness from high natural frequencies, and the cost of calculating the time-variate inverse matrix of inertia are focused. The system-level model reduction of the adaptive modal integration (AMI) is applied. By using AMI, the model is discretized and linearized throughout its movable configuration, then the dynamics model is presented in form of modal coordinates systems. The lowest 14 out of 26 mode shapes are selected to represent the flexible motion of the model. The mode shapes, and the inertia matrix and its inverse are precalculated and interpolated during the simulation. The reduced model is constructed such that it could be calculated with the arbitrary pattern of input motion. The numerical simulation is performed to compare the reduced model and the nonlinear model. The reduced model able to illustrate an accurate result under shorter calculation time. The truncation of high frequencies modes encouraged the larger integration step while the interpolation reduced the cost of calculating the inverse matrix are resulted in short calculation time.

In designing a large robot arm that possesses height of 10m or more, the increase of stress due to the weight of the robot is a big problem. In order to realize a large robot arm, a robot arm incorporating a Tensegric structure was proposed. Tensegric structures are already used in the field of construction where combination of compression members with wires are used to maintain their posture and control. In this research, we focused on the Tensegric unit that composes the robot arm by varying the lengths of wires, and analyzed the mechanical deformation due to the load by the mass of the entire arm. Tensegric unit is supposed to be made by combining cylinders and we investigated the relationship between the unit shape and mechanical deformation and sought the optimum unit shape that is strong against deformation. This research use the theoretical methods based on material mechanics to analyze the deformation such as bending, bending and buckling of the unit, and use a Tensegric arm with a total length of 4 m as a model. As a results of analysis, bending stress and bending can be suppressed by increasing the outer diameter and inner diameter of the cylindrical section of the unit. Then, it is proved that the load generated in the unit of the Tensegric robot arm is acceptable for general mechanical materials, and validity from a mechanical aspect of the Tensegric robot arm was proved.

This study proposes an active suspension that suppresses vehicle rolling oscillation under preview closed-loop finite-time settling control using rotational vibration manipulation function (rVMF) as a reference input. The active suspension operation is performed efficiently by using preview data on the road surface profile beforehand. A 1/2 car model was used in simulations. As a comparison, a 1/2 car model that is ideally controlled under sky-hook theory was considered. At each operational instant, the rolling oscillation of the car body was suppressed by driving two actuators under the base of the active suspension along rVMF. Under two different road surface profile in left and right, the rolling oscillation was well suppressed. On the other hand, sky-hook took more time to cease the vibration. However, since proposed method focused on the suppression for rolling oscillation, it cannot suppress vertical vibration of the car.

The insertion of elastic ferromagnetic substance into the gap has been proposed to increase the attractive force of a magnetic suspension for vibration isolation system. The vibration isolation system with a series connection of a positive-stiffness and a negative-stiffness suspensions (zero-compliance vibration isolation system) has been studied extensively. In this system, the isolation table does not displace when a static direct disturbance is applied on the table. A negative-stiffness suspension has been achieved by using zero-power control magnetic suspension. To increase the attractive force of the zero-power magnetic suspension system, the insertion of an elastic ferromagnetic substance into the magnetic flux path between an electromagnet and a suspension target has been proposed. The elastic ferromagnetic substance increases the suspension force with higher magnetic permeability than air. However, the zero-power magnetic suspension system with elastic ferromagnetic substance suffers from low-frequency self-oscillation due to friction. The amplitude of the self-oscillation has been halved by adding a dither signal to the control input. To reduce the self-oscillation more, a dead-band element is added in the controller. In addition, the amplitude of the self-oscillation is reduced by increasing the amplitude of negative stiffness. The basic characteristics of reducing the self-oscillation in the negative-stiffness and zero-power control system are studied experimentally in a single-degree-of-freedom magnetic suspension apparatus.

With the development of the automotive industry, consumers' interest in the emotional quality of vehicles has been increasing. The purpose of this study is to resolve the emotional discomfort for the detailed vibration transmitted from an accelerator pedal that is in direct contact with the driver in a vehicle. Therefore, an individual accelerator simulator for each axis has been designed and made in order to study for the foot sole sensitivity of the human body. A modal test about the mounts used for the simulators to avoid resonance occurred from the simulators has been performed, and accurate stiffness and damping values were extracted on the basis of the analysis of dynamic characteristic and its following frequency response. In the experiment of pedal vibration, the simulators were excited within specific range of frequency based on the analysis of plantar supporting structure against pedal effort and boundary conditions considering external influences. Accelerometers were attached to each of the axes of the simulator to measure the acceleration response for the vibration due to excitation. Then, it was verified that the magnitude of the target vibration within the operating frequency can be implemented. In addition, in the preliminary experiment, the effect of the magnitude of the vibration on each axial direction of the simulator was analyzed to investigate the sole sensitivity of the driver’s foot by frequency on account of RPM change while driving. To make the results from the experiment more reliable, the vibrations occurred from the different directions other than the target direction were minimized for each accelerator simulator by checking the crosstalk. Investigation of the foot sole sensitivity of human will be conducted through an actual experiment with test subjects in the future.

This study introduces simple piece-wise linearization in time series (SPLiTS) that is developed to estimate physical parameters of nonlinear structures based on a time-domain inversion. SPLiTS regards a nonlinear structure to be a set of piecewise linearised structures, based on each half-cycle wave in the displacement response data. SPLiTS minimises the effect of the central-point shift in displacement response data. It selects effective data for parameter estimations, by employing three thresholds for the displacement and velocity response data as well as the number of steps consisting of each half cyclic wave. Then, response data (acceleration, velocity and displacement and external force applied to the structures) processed by SPLiTS is applied to the time domain inversion to estimate physical parameter of the nonlinear structures. In this study, SPLiTS was applied to experimental data obtained from shaking table tests, in which a specimen imitating a one-storey structure clearly displayed inelastic behaviour. SPLiTS reasonably estimated its physical parameters that show increased damping and decreased stiffness in time series at the occurrence of yielding. This experimental verification demonstrated that SPLiTS is applicable to physical parameter estimations of structures damaged by earthquake excitations.

The results of classical Tikhonov regularization method to identify the impact force will always be stable signals. To solve this problem, this paper proposes a semi-cosine function fitting method (SCFF) which uses semi-cosine functions as the basis functions to fit impact forces, and combines genetic algorithm to optimize the parameters; The mathematical solution expression can be obtained without iterative calculation, and the calculation efficiency is high. In this paper, the numerical results of a truss structure show that SCFF method will obtain accurate solutions and it has good robustness which illustrates that SCFF method owns great engineering application prospects.

The purpose of this research is to develop a multi-degrees-of-freedom shaking table that can be used for the centrifugal loading test. We use a 6-degrees-of-freedom parallel link shaking table as a mechanism that satisfies the conditions of compact size, high rigidity, multi degrees of freedom. In a parallel link mechanism, since actuators are not mounted perpendicularly in each other, unintended motion often occurs (multi-axis interference problem). When the reference signal is limited to a sinusoidal wave, these interferences cause a periodic error. These periodic errors cause tracking performance deterioration and output exceeding reference signal. It is important for the shaking table to equip a controller that can follow reference motion accurately and safely. However, when a high gain feedback controller is applied to suppress these interference, stability of the control system gets worse. Therefore, in order to solve above periodic error problem, this paper proposes a method to generate the modified reference signal of the acceleration controller based on off-line Inverse Dynamics Compensation via ‘Simulation of feedback control system’(IDCS). Furthermore, this paper shows effectiveness of the proposed method by applying the method to the actual 6-degrees-of-freedom parallel link shaking table. From the experiments it is seen that the periodic error is suppressed and output signal can be accurately followed reference signal.

The importance of the inspection of concrete structures has recently increased because of the ageing of the structures and for the prevention of accidents. The commonly used methods for inspection include visual confirmation and hammering inspection. An inspector marks and sketches the types, scale, and positions of defects on the structures through drawing, and assesses the status of concrete structures based on the number, types, and scale of defects. However, while performing this task, several problems exist in terms of workload, inspection accuracy, and management. To solve these problems, the mixed reality (MR) technology is used. The functions of sketching on the MR device to reduce the burden of inspectors and overlapping an internal structure to a real structure are developed. MR is being widely applied and is attracting considerable attention because it improves work efficiency. However, MR has not been widely used for structural inspection. Therefore, the purpose of this study is to consider the novel application of MR in structural inspection and investigate its effectiveness. We use Microsoft HoloLens and consider the method of utilization of MR for visual confirmation, hammering inspection, and state assessment of structures. In particular, we consider the visualization of hitting point on hammering inspection, the function of sketching on the MR device, and the method of showing the obtained inspection information to the inspectors on the MR device. Thus, although MR has the potential to significantly reduce workload and improve inspection accuracy, its practical application necessitates the development of advanced technology.

In recent years, the decline in the number of agricultural workers and their aging have become serious issues in Japan. To solve these issues, a new agricultural approach known as “smart agriculture” that utilizes advanced technologies such as robotics and information and communications technology (ICT) has been developed. However, in the growth management of tomato cultivation, only a few tasks of the planting and harvesting activities are automated. If other tasks could be automated, heavy burden on farmers would be significantly reduced.

This study proposes an automatic tomato harvesting system that combines object detection using deep learning with RGB-D camera (Intel RealSense D415), a robot arm (UFACTORY xArm 5 Lite), and a universal vacuum gripper. Moreover, this system was developed using ROS which is an open source software.

To evaluate the efficiency of the system, harvesting experiments were carried out using two sizes of tomatoes. The experimental results showed that the system achieved a success rate of over 90% with an average total harvesting time of under less than 20 s per single fruit. However, in the case of tufted tomatoes, harvesting could not be performed using the current gripper shape and robot arm motion planning method. The results validated the feasibility of the automatic tomato harvesting system.

In this study, we manipulated translational and rotational overhead crane in experiment and simulation under open-loop finite-time setting control (oFTS control) or closed-loop finite-time setting control (cFTS control) using the rotational vibration manipulation function (rVMF). rVMF, which is a finite-time settling function for 1DOF undamped oscillator, was used as a reference input for each sequential piecewise operation. It was difficult to perform oFTS control in the experimental apparatus, because the damping coefficient of them were too large to be ignored. On the other hand, since we can hardly perform rest-to-rest motion of the rotational overhead crane under cFTS control by modifying the reference signal along sampled data from the apparatus at each operational instant, it showed certain robustness. However, there exists some disturbances, such as damping effect, centrifugal force, and static and dynamic friction and so on, it was difficult to perform the intended control.

Future aerospace structures, such as Mars aircraft and flapping wing aircraft, have deployable/foldable and thin plate-like components connected by hinge joints. A deployment simulation is necessary to design the structures. Multibody dynamics (MBD) to model the joints coupled with a nonlinear finite element method is an effective approach to perform the simulation. In this study, a plate element based on absolute nodal coordinate formulation (ANCF) is coupled with MBD. ANCF plate element can express large rigid body motion and large elastic deformation including wing-chord deformation, and thus it is suitable for modeling low aspect ratio and very thin wings. However, the ANCF plate element has highly nonlinear elastic force leading to computational inefficiency. To overcome this computational inefficiency, we modify the elastic force formulation of the ANCF plate element by taking advantage of the wing characteristic. By using the ANCF plate element with the modified elastic force, we simulate the deployment motion of a multibody system.

Accelerometer using zero-compliance mechanism is proposed. The zero-compliance mechanism is a series connection of a positive-stiffness suspension and a negative-stiffness suspension with the same amplitude of stiffness. In the proposed accelerometer, an inertial mass is suspended with this mechanism. Force acting on the inertial mass is proportional to the displacement of the connection point of two suspensions (detection point). The acceleration is given by dividing the force by the inertial mass. Therefore, the acceleration is estimated by the product of the displacement of the detection point and the amplitude of stiffness divided by the inertial mass. An experimental apparatus according to the principle is fabricated to study basic characteristics of the proposed accelerometer. To achieve the zero-compliance state, a voice coil motor is incorporated into the mechanism, and PID control is applied. In the experiment, static acceleration is given to the apparatus by gravity. The static acceleration measurement shows that the displacement of the detection point is proportional to the acceleration while the displacement of the point of force is virtually zero. A dynamic acceleration is also given to the apparatus. The measurement result shows that the acceleration estimated by the proposed method is almost same as that of a conventional servo-type accelerometer. These results demonstrate the feasibility of the acceleration measurement with a zero-compliance mechanism.

The hammering test is widely used as a non-destructive testing method for inspection of internal defects in concrete structures. In this paper, we use a rotary hammer instead of a conventional inspection hammer to improve the inspection efficiency and the hammering force variation. We propose a method based on the self-organizing map (SOM) for automatically distinguishing the defective parts from the healthy parts of concrete structures. The hammering test experiments of concrete specimens with artificial defects are conducted. The hammering sounds are measured with a microphone moving with the rotary hammering device. The frequency spectra of hammering sounds measured at the impact locations are used as input data for the SOM and the impact locations are partitioned into two groups of the defective and the healthy parts from the SOM results. The results show that for the frequency spectrum, a dominant peak frequency varies depending on the defect depth at the defective parts. After the SOM map is trained, the unit with the smallest average overall value has almost all the impact locations of the healthy parts. By removing the impact locations belonging to its unit, the impact locations corresponding to the defective parts are extracted. The extracted impact locations identify the exact locations and widths of the defects.

In this study, we propose a new method that is useful for estimating unknown parameter values of stochastic differential equation (SDE) models, based on probability density function (PDF) data measured from random dynamical systems. As our method does not require explicit description of PDF, it can be applied to the SDE models even when their PDFs are hardly derived in explicit forms due to multiplicative-noise terms, nonlinear terms, and so on. Therefore, our method is expected to provide a versatile tool to dynamically parameterize measured PDF data. In our proposed method, it is assumed that a measured PDF is obtained from a random dynamical system whose structure is described by a known SDE model with unknown parameter values. With the help of Itô calculus, the Fokker–Planck equation (FPE) is derived from the SDE model. The measured PDF and a candidate of parameter values are substituted into the FPE to calculate a FPE residual. Our method is applied to two random vibration systems. Their FPE residuals tend to zero as the parameter values tend to exact values, showing that our proposed FPE residual can be utilized for unknown parameter estimation of SDE models.

As robot arms used in industrial factories are required high-speed operations and precise positionings in order to improve work efficiency and accuracy, their residual vibration is one of the crucial problems in automation industry. Many robot arms use a reduction gear such as a harmonic drive for each joint. Since the harmonic drive is small in backlash but low in rigidity in rotational motion, most residual rotational vibrations are due to the spring-like behavior of the reduction gear. Moreover, since many robot arms have multiple joints, multiple vibration modes occur. However, most of the previous studies treat merely a fundamental mode vibration, and higher modes are merely suppressed under closed-loop control. In this study, we proposed a reference input of a finite-time settling function, called rotational vibration manipulation function, to suppress the residual rotational oscillation of the robot arm with the reduction gear as a rotational spring under open-loop control. The manipulation function is used in feedforward control for one-time rest-to-rest motion in various operational times. We performed simulations to discuss specific operational times that suppresses the both residual vibrations in the fundamental and secondary modes of a horizontal 2DOF robot arm simultaneously.

In the field of space engineering, it is one of the hot topics to extend the mobility of space exploration rovers. The ability to select the mobility autonomously according to the exploration environment enables the rover autonomous exploration mission without detailed command from the control center on the earth. This leads to a reduction in mission execution duration. In this study, the physical property of the exploration condition, that is, movement speed, friction, and gravity were parameterized in terms of mobility. We investigated the relationship between the appropriate mobility of the rover and physical properties through numerical simulations and hardware experiments.

In recent years, there is a large category of space-debris including decommissioned spacecraft on the earth orbit. It has become a severe problem in the field of space engineering because they might cause a serious crash to spacecraft. Therefore, it is an urgent problem that we need to retrieve or remove the decommissioned spacecraft on the earth orbit as soon as possible. To do that, it is an inevitable technique to specify the precise motion of the spacecraft. In this study, we aimed to propose a new method to specify the motion of decommissioned spacecraft based on real-time movies taken from other spacecraft.

The problems to be solved in this research are roughly divided into two. One is to accurately track and estimate the attitude motion of the target spacecraft. It is established by tracing the motion trajectory of the feature points of the target spacecraft on the captured image. The other problem is to estimate the three-dimensional attitude motion of the target spacecraft from the two-dimensional captured image.

In this paper, we propose a robust motion estimation method using Optical Flow to track the motion of the feature point of the target spacecraft, and Kalman Filter to estimate the 3D motion spacecraft, assuming that the motion of the target spacecraft is pure-spin. We report the results of numerical examples.

Toward an advanced speed railway system, there are ongoing extensive studies on each component of railway vehicles. Reducing the aerodynamic noise emitted from the pantograph heads is one of the most important subjects for high-speed railways from the environmental point of view. In order to reduce such aerodynamic noise, a suitable configuration of the pantograph head, which has a smooth cross-sectional profile, has been investigated. Furthermore, high-contact performance is desired in pantographs. Consequently, the contact strips are often supported by springs, to lighten mass which touch the contact wire directly. The pantograph head with a multi-segment slider is a practical example of this design. However, the pantograph head with a smooth cross-sectional profile and the conventional suspension system of the contact strip sometimes cause undesirable lift force characteristics as a result of the variations in the cross-sectional shape due to the operation of the suspension system. For this reason, authors have developed the multi-segment pantograph head, which employ novel suspension systems that prevent the abnormality of the lift force characteristic. This paper describes the mechanism of a multi-segment pantograph head and the validation results of the suspension system by bench test equipment with large current.

This paper describes vibration analysis methods using modal analysis for coupled vibration between an acoustic field and flexible structures. In particular, the case where flexible structures are installed inside of an acoustic field is described in this paper. Numerical analysis methods such as finite element method and finite-difference time-domain method have been used to analyze coupled vibrations. Spatial discretization is used in these numerical analyses; however, the proposed analysis methods can analyze coupled vibrations without using spatial discretization because the proposed methods use the superposition of the vibration modes of the original acoustic field as a continuous system. Mathematically, superposition of vibration modes is a kind of series. The coupled vibration is expressed by the series that corresponds to the superposition of the vibration modes in the proposed methods. Based on this concept, two methods are proposed in this paper: one is referred to as built-in method, and the other is referred to as binding method in this research. The characteristics of the flexible structures are built in the acoustic field in the built-in method. In contrast, the acoustic field and flexible structures are bound by sufficiently stiff elastic bodies in the binding method. The equations of motion of the analytical models were derived, and the effectiveness of the proposed method was verified through simulations.

The subject of this study is KORAD-21, a multipurpose dry cask storage capable of carrying out transportation, storage and disposal. The purpose of this study is to develop a methodology for engineering evaluation that sufficient structural safety can be maintained under various accident scenario conditions that can occur during storage and transportation. Especially, the structural response of the dry cask storage in drop situation was analyzed based on the finite element model. The responses of drop scenarios are investigated using an explicit nonlinear dynamic FE simulation with a three-dimensional detailed model of dry cask storage via commercial FE code LS-DYNA and Explicit dynamics of ANSYS. For the analysis efficiency, two FE models were constructed in consideration of the symmetry of geometry and load. First, the quarter model was constructed because the geometry and load were symmetrical in four directions in the case of 9m vertical drop. In the case of 9m horizontal drop and inclined drop, half model was constructed because the geometry and load were symmetric in both left and right directions. Both models applied symmetry constraints on the planes of symmetry. The analysis was performed at the initial velocity of 13.29m/s, which is the velocity just before the dry cask storage hit the floor. For the conservative analysis, the floor where the cask collides applied rigid body model to avoid penetration or energy absorption. The results of the 1/3 scaled model test and the analytical results of this study were found to be similar and consistent in trend. The validated analysis results can be used to evaluate the structural safety of the cask itself, and furthermore, the FE model can serve as the basis for the evaluation of cracks and corrosion under the dynamic load of drop accident scenario.

Nonlinear resonance of a cantilever beam under mechanical impacts is investigated experimentally for energy harvesting from human induced low-frequency vibration. In the prototype of this study, a metal ball is used to yield impulsive forces acting upon the cantilever installed in an electromagnetic type vibration energy harvester. A multipole magnet array attached on the cantilever moves above a planar coil fixed on the baseplate of the device, leading to power generation through electromagnetic induction. Due to the nonlinear excitation force arising from ball impacts, superharmonic resonance occurs at integer fractional frequencies of the cantilever’s natural frequency. Nonlinear response amplitudes of the cantilever and resulting induced voltage are measured under continuous sinusoidal excitation at 1-20 Hz. To explore resonance characteristic, we examine three cantilevers with different natural frequencies: 21, 34 and 76 Hz. In addition, the travelling distance of the ball is altered to realize maximum induced voltage. It is found that the travelling distance needs to be tuned depending on the natural frequency of the cantilever because there is an optimal distance for power generation. For a larger travelling distance, the induced voltage decreases. The critical distance can be numerically estimated by using the analytical model based on a single DOF damped mass-spring system. Combination of the frequency up-conversion technique and tuning strategy developed in this study offers a fundamental advantage for low-frequency vibration energy harvesting with compact device dimensions compared to the commonly used on-resonance harvesters.

A new model of magnetically levitated (Maglev) vertical axis wind turbines (VAWTs) is presented. The rotor is suspended by two permanent magnet (PM) attractive type passive magnetic bearings (PMBs), and the position control of one of the PMs is used to stabilize the axial motion of the rotor. The PM is supported by the two leaf springs and actuated by the two electromagnets to control its axial position. The proposed structure can support the rotor without mechanical contact and reduce the rotation loss. Moreover, it is possible to change the radial stiffness by changing the air gap between the rotor and two PMBs, provides the ability to avoid the resonance at the critical speed. In this paper, the structure of the proposed Maglev VAWT is introduced, and the mathematical model is derived. Then, the control method is discussed, and the local feedback loop strategy is introduced for easy gain tuning. The levitation and rotation are experimentally confirmed, and the results show that the stable levitation and rotation can be performed and the rotation loss is quite low.

Falls in people with walking disabilities lead to being bedridden and an increase in long term care. The prevention of these incidents is thus a key factor in maintaining activity level and maximizing their quality of life (QOL). One of the main causes of these incidents is hip fracture by sideways fall. Although the sagittal plane motion has been widely studied, there are few studies about frontal plane motion. In this study, we focus on frontal plane motion and consider fall prevention by plantar height. Falls may occur when the center of gravity (COG), which is followed by the ground reaction force, is shifted from the base of support. The focus of this study is to utilize insole treatment used in physiotherapy, which adjusts the plantar height to change the direction of the ground reaction force so as to maintain balance during walking. The purpose of this paper is to assess the effect of plantar height by magnetorheological (MR) fluid brake on fall prevention. We proposed a theoretical model combining a self-righting doll and an inverted pendulum. The model’s validity was verified by comparison with the motion of a developed leg foot model. This paper indicates the motion of the leg foot model is close to the simulation in which the model changes from the self-righting doll to the inverted pendulum. Moreover, the plantar height on the outside of the foot is effective in fall prevention because the direction of the torque changes in the opposite direction to the fall by switching to the inverted pendulum model.

For vibration control of structural system, semi-active control is expected to show better performance than other control methods in terms of energy efficiency. However, because of the energy dissipation characteristics of the semi-active control devices, the mathematical model of the semi-active control system becomes a hybrid model. Optimal control of hybrid models can be solved by mixed integer quadratic programming. However, this method is computationally expensive because the optimization problem must be solved for every sampling instant. One such computationally inexpensive method is clipped-optimal control, but its performance is not guaranteed because it does not consider the constraints of energy dissipation of the semi-active device. The clipped-optimal control can be expressed as a switching system of three systems under the influence of energy dissipation constraints. In a 1-DOF (degree of freedom) system, the switching conditions of the three systems can be expressed as angles on a phase plane. The 1-DOF vibration system draws an ellipse in the forced vibration and a spiral in an initial response on the phase plane. In the case of a vibration system that draws a circle-like trajectory on the phase plane, unlike other switching systems, the selection of these three systems is performed at a substantially constant rate. In this study, we propose a semi-active control method using a single linear system composed of the above three systems. The linear systems are referred to as the averaged systems in the study. We propose a method to systematically design the clipped-optimal control, which has been conventionally designed by trial and error, with the averaged system. Simulation studies show the effectiveness of the proposed semi-active control approach.

With zero-power control, the multiple electromagnets system cannot realize level levitation when an eccentric load is applied, which may reduce the safety of levitation. This paper proposed anti-tilt and zero-power control to improve the performance of the magnetic levitation system with two rotatable magnets and one stable HEM. The moment caused by the eccentric load can be eliminated by an angular drive of the electromagnet. To estimate the rotation angle, this paper focuses on designing the controller based on the system model. The simulation results indicate that the zero-power levitation without tilt can be realized and the system performs similarly well for different load positions

The purpose of this research is to realize a large-scale robot arm. One of the author presented an idea to utilize tensegric structure to realize large-scale robots. Tensegric structure is made of multi-stage compression members, joints that connect them and tension wires connecting compression members to shape robot arm. This structure was proposed by Professor Saito of the Faculty of Architecture, Nihon University in a broad sense of the tensegrity structure. By changing the length of wires, it can be applied as robot arm. To examine the stability of multi-stage tensegric robot arm, experimental analysis using scaled model is carried out. In this experiment, we aim for a large robot arm of 20 m, but since it is difficult to reproduce it in reality, we use a model reduced to 1/10. The unit at this time is a unit created from a 3D printer using a PLC. Twenty models of this model are connected and experimented in two ways to investigate attitude control under static conditions. The first method is to give a restoring force by using a piano wire in the joint part. The second method is to generate tension by hanging a weight on the wire. According to experimental analysis, Tensegric arm with 5 stages can change configuration freely to some degree while the arm with 7 stages possess quite unstable. Moreover, beyond 8 stages, the Tensegric arm could not withstand the load and collapsed.