This paper presents a disturbance-force compensator for an electrodynamic shaker. The characteristics of a shaking system are considered to be nonlinear and variable because of the influence of the test piece. In order to compensate for this problem, the influence of the disturbance force needs to be suppressed. The controller is designed using μ-synthesis by considering the uncertainty of the shaker. In order to investigate the control performance in relation to the influence of friction and sloshing, time waveform replication testing is executed. Finally, because the compensator suppresses nonlinearity, a good performance can be realized, as confirmed by experiments conducted using actual equipment.

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Master-slave control is becoming increasingly popular in the development of robotic systems which can provide rehabilitation training for hemiplegic patients with a unilaterally disabled limb. However, the system structures and control strategies of existent master-slave systems are always complex. An innovative master-slave system implementing force feedback and motion tracking for a rehabilitation robot is presented in this paper. The system consists of two identical motors with a wired connection, and the two motors are located at the master and slave manipulator sites respectively. The slave motor tracks the motion of the master motor directly driven by a patient. As well, the interaction force produced at the slave site is fed back to the patient. Therefore, the impaired limb driven by the slave motor can imitate the motion of the healthy limb controlling the master motor, and the patient can regulate the control force of the healthy limb properly according to the force sensation. The force sensing and motion tracking are achieved simultaneously with neither force sensors nor sophisticated control algorithms. The system is characterized by simple structure, bidirectional controllability, energy recycling, and force feedback without a force sensor. Test experiments on a prototype were conducted, and the results appraise the advantages of the system and demonstrate the feasibility of the proposed control scheme for a rehabilitation robot.

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This paper is presenting a method to generate online running trajectories that can be applied to bipedal humanoid robots. The proposed method is based on maintaining the overall dynamic balance by using the ZMP stability criterion throughout support phases. To be able to reach this goal, we utilize ZMP equations in spherical coordinates, so that the rate change of angular momentum terms in ZMP equations are included naturally by using Eulerian equations of motion for unsymmetrical bodies. Thus, undesired torso angle fluctuation is expected to be more restrainable comparing to other methods in which angular momentum information is ignored or zero-referenced. Moreover, we employ projectile motion dynamics throughout flight phases. Applying the aforementioned technique, we simulated bipedal running motion on a dynamic 3-D simulator. In conclusion, we obtained repetitive and successful running cycles which consistently verify the proposed method.

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In an autonomous mobile robot, ultrasonic time-of-flight (TOF) ranging systems are widely used for distance measurements. However, ultrasonic TOF ranging systems tend to neglect infinitesimal reflected waves below a threshold level. Therefore, we have proposed an integration-type ultrasonic wave sensor that utilizes the integration value of the sonar's reflected wave to recognize a traversable area for an autonomous mobile robot. The proposed method simultaneously determines the path and velocity; however, the calculated velocity varies significantly because of sensor noise or error. This paper presents a novel approach to filter the velocity by considering the accelerated velocity. This enables us to consider the limitation of the force exerted by the robot. The validity of the proposed method is investigated in various environments by applying this method to an autonomous mobile robot.

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Steer-by-Wire (SBW) system has a mechanical feature that the conventional mechanical linkages between the steering wheel and the front wheel are removed, and is operated by electric actuators. SBW system suits for active steering control improving vehicle stability, dynamics and maneuverability and so on. With conventional controller for SBW system, it is difficult for driver to feel reaction torque exactly from steering block. In this paper, a new SBW system of electric vehicle based on bilateral control designed by passivity approach is proposed. At first, conventional bilateral control scheme using disturbance observer is reexamined. Secondly, a novel bilateral control with passivity is introduced. We also make clear the performance of the proposed control scheme and compare it with conventional bilateral control scheme. Finally, the effectiveness of the proposed method is demonstrated by experiments with the electric vehicle.

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An electric active stabilizer suspension system has been developed as a technology for controlling vehicle roll. The system includes various sensors that detect the vehicle's running state, and active stabilizer actuators that use electric motors and reduction gears to control roll. The electric stabilizer suspension system was compared with hydraulic stabilizer systems, and an investigation demonstrated the superiority of the developed system, which offers outstanding vehicle behavior, improved responsiveness and reduced energy consumption (including energy regeneration).

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Several former top players sent a letter to the International Tennis Federation (ITF) encouraging the governing body to revisit the question of rackets. In the letter, the players wrote that racket technology has led to major changes in how the game is played at the top level. This paper investigated the physical properties of a new type of racket with active piezoelectric fibers appeared recently in the market, and predicted the various factors associated with the frontal impact, such as impact force, contact time, deformation of ball and strings, and also estimated the racket performance such as the coefficient of restitution, the rebound power coefficient, the post-impact ball velocity and the sweet areas relevant to the power in tennis. It is based on the experimental identification of the dynamics of the ball-racket-arm system and the approximate nonlinear impact analysis with a simple swing model. The predicted results with forehand stroke model can explain the difference in mechanism of performance between the new type racket with active piezoelectric fibers and the conventional passive representative rackets. It showed that this new type racket provides higher coefficient of restitution on the whole area of string face and also gives larger rebound power coefficients particularly at the topside and bigger powers on the whole area of string face but the difference was not so large. It seems that the racket-related improvements in play are relatively small and the players themselves continue to improve, accordingly there is a gap between a perception and reality.

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This study develops a hybrid damper for multi-modal vibration by combining an elastomer and a piezo ceramic element. The basic idea is to obtain satisfactory damping in the low frequency range, where elastomer does not work well, by introducing a piezoelectric element. In this hybrid damper, the elastomer comprises a dynamic absorber with a metal plate of small mass that deals with higher-frequency vibration, while piezo ceramic comprises a shunt damper with an electric shunt circuit that works for lower-frequency vibration. The effectiveness of this approach is examined through vibration control of a cantilever beam. The aim is to suppress the 1st mode vibration with the shunt damper and the 2nd mode with the dynamic absorber. With appropriate tuning procedures for the control parameters, vibration suppression of more than 10dB is attained in each mode.

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We propose a semi-active control of civil structures based on a one-step-ahead prediction of the seismic response. The vibration control device (VCD), which has been developed by authors, generates two types of resistance forces, i.e., a damping force proportional to the relative velocity and an inertial force proportional to the relative acceleration between two stories. The damping coefficient of the VCD can be changed with a command signal to an electric circuit connected to the VCD. In the present paper the command signal for changing the damping coefficient of each VCD is assumed to take two values, i.e., the command to take the maximum or minimum damping coefficient. The optimal command signal is selected from all candidates of command signals so that the Euclidean norm of the one-step-ahead predicted seismic response, calculated by a numerical integration, is minimized. As an example a semi-active control of a fifteen-story building with three VCDs is considered. The simulation results show that the proposed semi-active control achieves superior performance on vibration suppression compared with a passive control case where the damping coefficient of each VCD is fixed at its maximum value.

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In recent years, various kinds of robot systems have been developed, and various kinds of locomotion methods have been developed for them. One of the locomotion methods is the hopping locomotion method, which exhibits high performance in the fields with rough terrain and uncertainties because it does not require continuous contact with the ground during locomotion. Utilizing resonance in the hopping mechanism should have a beneficial effect on energy consumption and downsizing the system. In this study, in an attempt to utilize resonance for the hopping mechanism, a hopping phenomenon induced by resonance is analyzed; the analysis reveals that a simple resonance of the system results in an insufficient hopping height due to insufficient energy stored by the resonance. The analysis further reveals that dividing excited components and separately exciting them enable the storage of greater energy via resonance than simple excitation. Based on the analysis, this paper proposes an effective energy-storing method for the hopping mechanism through the use of resonance. The effectiveness of the proposed method is confirmed by numerical analyses and experiment.

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In order to improve the traveling performance of robotic system in the fields with rough terrains and uncertainties, the hopping mechanism is sometimes employed as a locomotion method. In our preceding study, a hopping mechanism utilizing the energy generated by resonance is proposed, and we revealed that simple resonance of the system resulted in insufficient hopping height and that some additional devices were required to obtain a meaningful hopping height of the system. In this paper, a hopping mechanism with stiffness switching is proposed to achieve a meaningful hopping height. The stiffness is switched by an electrical method through the use of piezoelectric elements and capacitors connected to it. It is expected that the proposed mechanism leads to a realization of a smaller and more reliable hopping mechanism since it has quite simple configuration. The proposed mechanism is analyzed theoretically and the effectiveness of the mechanism is confirmed by numerical analyses.

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This paper deals with deriving a simple linearized equation of motion for axisymmetric tops spinning on a table; the equation includes the effects of both friction and gravitation. The derived equation is a single second-order equation with complex number coefficients. The main variable is the inclination angle of the spinning axis, which is expressed by a single complex number. No Euler's angle is used. The precondition for linearization is that both the angular momentum vector and the spinning axis are close to the zenith direction. The friction is assumed to be viscous, and the friction torque can be expressed by using the height of the gravity center and the radius of the curvature at the contact point to the table. Two eigenvalues for the equation give a deep insight into the attitude behavior. The root-locus method was applied to explain the spinning motion stability of various axisymmetric bodies. An analytical solution for a horizontally suspended spinning top is given to show that the locus of the spinning axis is a trochoid.

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This paper describes a vibration analysis study using the finite element method (FEM) for two viscoelastic blocks connected by a nonlinear concentrated spring. One of these blocks is supported by a linear concentrated spring. The restoring force of the spring is expressed as a power series of the relative displacement between the blocks. This restoring force includes linear hysteresis damping. Therefore, a complex spring constant is introduced for the linear component of the restoring force. The finite elements for the spring are expressed and they are attached to the viscoelastic structures, which are modeled as linear solid finite elements. The discrete equations in terms of physical coordinates are transformed into nonlinear ordinary coupled equations using normal coordinates corresponding to the linear natural modes. These transformed equations are then computed to obtain the nonlinear frequency responses with a fairly small degree of freedom. The effectiveness of this analysis is checked using a basic mass-spring model. Moreover, the influences of the storage modulus of the blocks on the nonlinear responses are clarified. Further, the influences of the dissipated energy on the nonlinear frequency responses of the viscoelastic blocks are investigated.

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In this study, we estimate an efficient layout of sound absorbing materials in three-dimensional spaces. For this purpose, we use damping contributions with eigenvectors as weight coefficients. Three-dimensional finite Elements of absorbing materials are modeled using a complex effective density and a complex bulk modulus of elasticity. By expanding the solution of complex eigenvalue problem with a small parameter related to damping, we derive the first order approximate equations of motion with respect to the small parameter. From these equations, the contribution of each element to modal damping is derived in consideration of multiple modes. The sound absorbing materials are arranged in three-dimensional spaces according to this contribution and by considering the components of eigenvectors at the evaluation points as the weight coefficients. The effectiveness of this method is verified using an expanded chamber.

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Seal stability is often evaluated by Whirl frequency ratio (WFR) and Effective damping coefficient (C_eff) calculated on the assumption of synchronous whirl. However, the natural frequency of the rotor system must be used for calculation of WFR and C_eff when determining self-excited vibration. This paper discusses the evaluation of seal stability using WFR and C_eff. First, the stability analysis is performed by FEM for a simply supported Jeffcott rotor model, having a seal near the disk. Next, WFR and C_eff are calculated for the following two frequencies; (1) the natural frequency of the rotor system, (2) rotational frequency. As the reference of stability, the logarithmic decrement is used for comparing with WFR and C_eff. Effective damping coefficient (C_eff) calculated using the natural frequency of the rotor correctly estimates the seal stability. Whirl frequency ratio (WFR) for the natural frequency of the rotor can judge the rotor stability, but cannot evaluate how good the seal is. Both C_eff and WFR calculated by using the rotational frequency cannot give correct criterion for the rotor stability.

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In order to clarify the mechanism by which the lung airway narrows during an asthma attack, dynamic buckling analysis of the wall was conducted. The wall was modeled using a visco-elastic thin-walled circular cylinder of the Voigt model for the planestress state. A governing equation for dynamic buckling was derived, and in the equation, the contraction of smooth muscle was replaced by uniform inward transmural pressure. The non-dimensional parameters for the buckling wave number n were nondimensional retardation time τ, non-dimensional increasing velocity of inward transmural pressure β, thickness radius ratio α², radius length ratio η, density ratio ζ, and Poisson's ratio ν. The validity of the theoretical model was confirmed by comparing the calculated wave number with that obtained from the experiment, in which a silicone rubber tube blended with silicone potting gel was used as the in vitro airway model. In addition, the wave number n increased with β. It was necessary to consider the damping effect of the tube model or the airway wall, and n increased by 1.5 to 2 due to the additional mass effect of surrounding tissues of the basement membrane in the airway wall.

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The seismic response of the structure is nonstationary random vibration because earthquake excitation is nonstationary random vibration. Calculating method for the statistical characteristics of such a nonstationary response is complicated. The mean square value of the response is usually used to evaluate the statistical characteristics of random response. Integral of the mean square value of the response corresponds to total energy of the response. In this paper, a simplified calculation method to obtain integral of the mean square value of the nonsatationary response is proposed. In this method, the mean square value of the stationary response is used. As an earthquake excitation, nonstationary filtered white noise is used considering the dynamic characteristics of the ground. Integrals of the mean square value of the nonstationary random response are calculated for various values of parameters. It is found that the proposed method gives exact values of integral of the mean square value of the nonstationary random response.

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A railway is organized by a variety of individual technologies, and functions safely and properly as a system, therefore it is necessary for the system safety to study each potential case of disasters caused by earthquakes. Recent reports indicate that railway vehicles could be derailed solely by the ground motions of earthquakes with no fatal damages of vehicles or tracks. Based on the reports and facts, we believe that we should further study the derailment mechanism of a high speed railway vehicle excited by large seismic motions, to pursue to minimize the risk of railway system against large earthquakes. At the start of the study, we developed our original vehicle dynamics simulation and then employed it for numerical analyses. At the present stage, through the analyses, we obtained the following major outcomes. (1) Most of derailments are brought as the result of the rocking motion of a vehicle by track excitations underneath. Interestingly, the derailing motions are observed similarly regardless of vehicle speed. (2) By contrast, the excitation amplitudes for derailment are influenced by vehicle speed particularly in lower input frequencies. This can be explained by the sensitivity of the relative wheel/rail slide due to creepage. (3) The excitation amplitudes for 30mm of wheel lift are relatively independent of vehicle speed. (4) The wheel/rail slide strongly depends on the friction coefficient if a vehicle stationed, being relatively independent of the friction coefficient at higher speeds.

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A railway is organized by a variety of individual technologies, and functions safely and properly as a system, therefore it is necessary for the system safety to study each potential unsafe case caused due to large earthquakes. Recent reports indicate that railway vehicles could be derailed by earthquake ground motions with no fatal damages of vehicles or tracks. Thus, we should further study the derailment mechanism to pursue to minimize the risk of railway system safety against large earthquakes. Particularly, for more comprehensive understanding on the derailment mechanism of high speed railway vehicle, the derailment process of the case should be directly verified. Therefore, in this study, we arrange an experimental setup with 1/10 scale vehicle and roller rig providing both conditions of high speed wheel/rail rolling contact and large amplitude excitations. Through the experiment, we obtained the outcomes. (1) Two types of vehicle derailment motions are observed; one is rocking derailment and the other is sliding derailment. Derailment motions are similar regardless of vehicle speed. (2) By contrast, the excitation amplitudes for derailment decrease according to the increase of vehicle speed particularly by low frequency excitations. (3) The excitation amplitudes for wheel lift of flange height are relatively independent of vehicle speed. (4) Based on the similarity of fundamental vehicle dynamics between the 1/10 and full scale vehicles, those observed mechanisms in the scaled test should be applicable to that of full scale vehicle.

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