This paper deals with vibration problems and a model based vibration control strategy for large-scale structures like long bridge towers, high-rise buildings, huge earthquake testing facilities and space structures. When resource and energy savings expenditure is required, the problem of weight increase has become an inescapable point in the construction of these large-scale structures. In order to reduce weight, flexible structures in becoming lightweight tend to be susceptible to more vibration problems. In this paper, after informing a lumped mass modeling approach form continuous structures, it is introduced that this approach is suitable to control vibrations for large-scale structures

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This paper describes the present state of research and development for civil use autonomous unmanned aircraft. In particular, the history of civil use UAVs, the research and development in the world and in Japan, and the subjects and prospects for control and operation systems of civil use autonomous UAVs are described.

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The range of applications using microvibration isolation equipment is being extended to devices for which the influence of vibration had not previously been considered. As a representative example, the application of active microvibration isolation equipment using an air spring actuator, suitable for MRI and NMR that operate in a strong magnetic field, is examined. In order to be used in a strong magnetic field, the active microvibration isolation equipment needs to have an actuator made from a nonmagnetic material. The servo valve that controls the air pressure in the actuator, however, must be installed away from the strong magnetic field since it cannot be fabricated from a nonmagnetic material. This necessitates the use of a long air supply tube to connect the servo valve to the actuator. Since this long tube affects the actuator characteristics, adequate vibration isolation performance cannot be attained with a controller designed using the conventional equipment model. In this study, a new equipment model is proposed by analyzing the characteristics of the active microvibration isolation equipment, and the control system is designed for the model using the model matching technique. The equipment model and control technique are validated by simulation and experiment.

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When large external forces come from the road, a suspension stroke reaches its limitation and riding comfort may decrease. To overcome this problem, we propose a new control method for an active suspension that can avoid reaching the stroke limitation. A sliding mode controller is designed by considering the rigidity variation of a spring. Also, in order to estimate the internal state of the suspension, a variable structural system (VSS) observer is designed without the information of nonlinear force occurring in the rigidity variation when the suspension reaches the stroke limitation. By carrying out simulation and experiment of a quarter-car model, it is verified that the performance of the controller is superior to that of the method, which switches to a passive damper near the stroke limitation from a linear quadratic regulator (LQR) in a small stroke range.

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A novel magnetic suspension system with three flux-path control modules was developed. The module consists of a ferromagnetic plate, a voice coil motor (VCM) for driving the plate and a displacement sensor for detecting the position of the plate; the sensor is comprised of a V-shape plate spring and four strain gauges pasted on it. The ferromagnetic plate is inserted into the gap between a permanent magnet and a suspended object (floator). The lateral position of the plate is controlled by using the VCM and the sensor. Since the flux from the permanent magnet to the floator varies according to the position, the amplitude and direction of the attractive force acting on the floator can be adjusted with multiple modules. Stable suspension was achieved by applying PD control. A fluctuation was observed in the position of the floator. It was reduced by feeding back the lateral motions of the floator. The two-dimensional and three-dimensional noncontact manipulation of the floator was also achieved in the developed magnetic suspension system.

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This paper presents a nonlinear controller for electric power assist systems based on the sliding mode control. The proposed sliding mode controller is designed to achieve desired nonlinear properties including gravitational effect with robustness against disturbances such as friction force and modeling errors. Furthermore, so-called reaching phase is positively utilized so that the operator can feel disturbance torque of relatively large amplitude which should be noticed as information about environment, for example, when hitting an obstacle accidentally. Although the reaching phase can be designed from several points of view, the dynamics in the reaching phase is linearlized in order to use fruitful linear control theories such as H-infinity theory.

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For studies of biped walking robots, energy-efficiency is an important issue. We have proposed an optimal-trajectory planning method based on a function approximation method, and applied it to a 2D biped walking model. With this method, we obtained the solution of minimal square integration value of the input torque. Previously in the literature, this method included only an equality state constraint. However, in this paper, we include an inequality state constraint to restrict the joint-angle range. In addition, walking experiments were performed to verify the effectiveness of this method. Results showed that stable walking of a 0.6 s period and 0.3 m/s speed was realized. Finally, we evaluated the robot's energy-efficiency using Specific Cost analysis.

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In this paper, we proposed a robust control method based on the virtual suspension model for keeping the posture stability and decreasing the tiny vibration of the robot body when it is walking on irregular terrain. Firstly, we developed a six-legged walking robot for this study based on stable theory of wave gaits and CAD dynamic model. Secondly, in order to keep the posture stability of body when robot walks, we designed a virtual suspension model with one degree of freedom, which has virtual spring and damper, for the direction of the center of gravity, the pitch angle, and the roll angle of body respectively. And then, in order to decrease the tiny vibration of body when robot walks, we proposed an active suspension control by using sliding mode control based on a virtual suspension model. These proposed methods are discussed using the walking experimental results of the developed six-legged walking robot.

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Ultrasonic dental scaler is an instrument to remove dental calculi using ultrasonic vibration of a transducer. The conventional transducer has a hose to provide water to scaling point. The hose causes attenuation of the ultrasonic vibration. This paper describes a new transducer design to avoid the attenuation. Design decision by comparison of two types of transducer designs is reported. Additionally, the ultrasonic transducer is used in resonance condition. The resonance frequency, however, is shifted according to value of input voltage to the transducer and condition of contact with tooth or gum. This paper presents a resonance frequency tracing system to solve the frequency shift. Step responses are specified as evaluation of the system. Application of the system to diagnosis is also discussed. Experiments on measurement of object properties are reported. The results indicate possibility that dental health can be investigated by observing the frequency shift during the scaler operation.

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This paper analyzes the fundamental dynamic characteristics of a tilting railway vehicle using a variable link mechanism for compensating both the lateral acceleration experienced by passengers and the wheel load imbalance between the inner and outer rails. The geometric relations between the center of rotation, the center of gravity, and the positions of all four links of the tilting system are analyzed. Then, equations of the pendulum motions of the railway vehicle body with a four-link mechanism are derived. A theoretically discussion is given on the geometrical shapes employed in the link mechanism that can simultaneously provide zero lateral acceleration and zero wheel load fluctuation. Then, the perfect tilting condition, which is the control target of the feedforward tilting control, is derived from the linear equation of tilting motion.

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To improve the riding comfort of railway vehicles equipped with the air suspension system now in widespread use, we tested a semi-active air suspension control system with a variable orifice. The system is installed between the air spring and the auxiliary air chamber, and is adjusted using a controller with a design based on the H_∞ control algorithm. We carried out numerical simulations using a half railway vehicle model with a 4-element air suspension model, as well as performing excitation tests using a half carbody at a rolling stock test plant. The results show that the proposed system effectively reduces the power spectral density (PSD) of acceleration of the carbody floor. Additionally, little difference was observed between the vibration mitigation effectiveness of a reduced-order controller and that of the original one.

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Suppression of the vertical bending vibration of carbodies has recently become essential in improving the riding comfort of railway vehicles. In many cases, the resonant frequency of the system (consisting of a bogie frame and axle springs) is close to that of the first mode bending vibration of the carbody, so suppressing the vibration of bogie frames near their resonant frequency effectively reduces carbody vibration. In this paper, we propose a method of suppressing such vibration by controlling the damping force of axle dampers installed between bogie frames and wheel sets. The design of the semi-active controller applied to determine the optimal damping force is based on the sky hook control theory. Numerical simulations using a vehicle model with 16 degrees of freedom as well as excitation tests using a carbody with variable axle dampers at a rolling stock test plant were carried out. The results show that this control method effectively reduces the power spectral density (PSD) of acceleration on the floor and that the riding comfort level (L_T) can be improved by about 3 dB.

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This paper describes a pointing control of a mobile antenna mounted on a vehicle. For precise pointing, the antenna must be controlled to point to a target under the influence of continuous disturbances acting on the vehicle. For this purpose, we propose an optimal controller design method in a framework of the H_∞ gain-scheduled controller synthesis. By this synthesis, the optimal controller is obtained by using parameter varying notch-filter in order to attenuate the various frequency disturbances. We apply this design method to an automobile model having a rotating antenna.

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In this paper, a new active suspension control scheme is developed so that ride comfort becomes best at any specified location on vehicle body. To achieve this end, two ideal vehicles are designed in which ride comfort becomes best at each different location. Then, linearly combining the two ideal vehicles, a combined ideal vehicle is constructed. It should be noted that we can easily force ride comfort at a specified location become best in the proposed combined ideal vehicle by setting only one design parameter. To achieve the good property stated above in actual vehicles, a robust tracking controller is proposed. It is shown by carrying out numerical simulations that ride comfort at a specified location can be easily improved in the closed loop system using the proposed combined ideal vehicle.

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Pneumatic muscle actuators (PMAs) have the highest power/weight ratio and power/volume ratio of any actuator. Therefore, they can be used not only in the rehabilitation engineering, but also as an actuator in robots, including industrial robots and therapy robots. It is difficult to achieve excellent tracking performance using classical control methods because the compressibility of gas and the nonlinear elasticity of bladder container causes parameter variations. An adaptive fuzzy sliding mode control is developed in this study. The fuzzy sliding surface can be used to reduce fuzzy rule numbers, and the adaptive control law is used to modify fuzzy rules on-line. A model matching technique is then adopted to adjust scaling factors. The experimental results show that this control strategy can attain excellent tracking performance.

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This work develops a dual-controller composed of a macroscopic controller (MAC) and a microscopic controller (MIC) for improving motion precision of a linear-motor-driven motion system. Based on the macroscopic model in which Coulomb friction model is considered, the MAC is designed. In the presliding region however, the MIC design is based on the lineralized microscopic model. Furthermore, a switching algorithm is developed for bumpless transfer in shifting control action between two controllers. Thus, when the table of motion stage moves to the desired position, the control action can be smoothly switched from the MAC to the MIC. The whole system with the proposed dual-controller has the advantage that it serves as a long stroke (coarse stage) and a short stroke (fine stage) to achieve high precision motion control. The experimental results reveal that it totally takes 2.59 seconds to reach the 1000μm target position with the accuracy of one BLU (basic length unit; sensor resolution), 20nm; the result has over 29% improvement when compared with the result using single MAC. In addition, good nanometer-scale tracking performance with the accuracy of one BLU, 20nm, can be obtained by using the MIC.

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It is performed to suppress the transverse vibration of the elevator ropes on a high-rise building caused by resonance between building-sway and rope-sway. The elevator rope has the characteristics due to its flexibility and length-varying and some constraints for the active vibration control. Hence, for compensating the influence of the time-varying characteristics and spillover, the nonstationary robust controller which has the robustness against unstructured and structured uncertainties is employed for the active vibration suppression of the rope. The suppression and robust stabilizing performances of the controller are demonstrated through the numerical calculations for the case in which the building is subjected to the ground disturbance like an earthquake and the tension of the rope varies. Thereupon, the control input system actuated by an alternate current motor is located right below the traction sheave and then it moves the rope directly in the presence of gaps between the rope and actuator. Consequently, the nonstationary robust controller shows the advantages in terms of the robustness on the uncertainties and the performance as compared to the optimal controller; and then it can adequately suppress the transverse vibration of the rope.

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Active magnetic bearings (AMB) have been widely used in various kinds of rotating machinery. However, since the magnetic force is nonlinear, nonlinear phenomena may occur when the rotating speed becomes higher and delay of control force increases. In this paper, the magnetic force is modelled to include the effect of the delay of electric current for control, and the AMB force is represented by a power series function of the electric current for control and shaft displacement. The nonlinear theoretical analysis of vertical rigid rotor-AMB system is demonstrated. The effects of the delay of electric current for control and other AMB parameters on the nonlinear phenomena are clarified theoretically and experimentally.

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A ball bearing reaction wheel (RW) is a key attitude control actuator of spacecrafts, but it is also a major source of inner disturbances. Future space mission requires high attitude stability, and disturbance property of the RW must be improved. There are some disturbance sources inside the RW, and abnormal motion of a retainer is one of the most significant ones. The retainer is one of mechanical parts of a ball bearing supporting a rotor spin axis. It is used to keep the ball intervals. Therefore it is nonholonomically constrained with balls, an inner race, and an outer race, and its complex motion causes disturbances which are difficult to be effectively removed. In this paper, dynamics of the retainer is investigated through experimental tests and numerical simulations. Disturbances of normal and abnormal RWs are compared, and relation between retainer mass imbalances and their dynamics are investigated. As results, a trade-off relation between instability reduction and disturbance reduction is verified and one of the criteria to decide the appropriate mass imbalance is proposed.

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The static and dynamic problems of structural and mechanical systems subjected to certain external excitations are established by a mathematical system consisting of static or dynamic equations and prescribed constraint conditions. The constrained behavior depends on the exact calculation of constraint forces required for satisfying the constraints. The generalized inverse method, which is one of many approaches to describe the constrained static or dynamic responses and takes an explicit equation form, does not require any numerical scheme to determine unknown multipliers but it was derived under the assumption of elastic systems. The static or dynamic responses beyond linearly elastic range also must satisfy the constraints themselves as well as the load-deformation relation. This study presents an analytical method to describe the constrained behavior beyond linearly elastic range, provides the mechanical meanings that the generalized inverse method has, and illustrates the validity of the proposed method through applications. And it is evaluated that the fundamental mode of dynamic system is constrained by the eigenvectors corresponding to the lowest eigenvalue of stiffness matrix at static equilibrium state.

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A new type of microperforated panel absorber (MPA) that has holes of multiple sizes instead of uniform size is experimentally investigated. The objective of this research is to obtain a wide band sound absorber that is thin, durable, clean, and healthy. The first step of this research is to investigate the performance of MPA having two different sizes and the same numbers of holes. The investigation is then extended to a combination of three and four different sizes of holes with various spatial arrangements and various densities or percentages of each size of holes on panels. The hole diameters vary between 0.4 mm and 1 mm and the cavity depths vary between 10 mm and 15 mm. The results show that a multi-size MPA enhances the absorption rate and widens the effective frequency band. This study also proves that a multi-size MPA when compared with a uniform size MPA has better sound absorption characteristics with respect to the absorber thickness and absorption bandwidth. These results make it possible to build thin, single layer sound absorbers that are effective in wide frequency bands and have the advantage of being tunable.

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This paper showed the damping effect and the vibration analysis of a shaft-disk-blade system with viscoelastic layers on blades. The focus of the research is on the shaft's torsional vibration and the blade's bending vibration. The equations of motion were derived from the energy approach. This model, unlike the previous, used only two displacement functions for layered blades. Then, the assumed-modes method was employed to discretize the equations. The analyses of natural frequencies damping property were discussed afterwards. The numerical results showed the damping effects due to various constraining layer (CL) thickness and viscoelastic material (VEM) thickness. The research also compared FRF's of the systems with and without viscoelastic layers. It is concluded that both CL and VEM layers promote the damping capability but the marginal effect decreases with their thickness. The CLD treatment also found drop the natural frequencies slightly.

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Systems with slight Coulomb friction at a supporting point have a very small dead zone in which the system stops after free oscillation. The small stiffness makes the dead zone very wide, even under slight Coulomb friction, because it is determined according to the ratio between Coulomb friction and stiffness. Results of a previous study clarify both theoretically and experimentally that in the neighborhood of buckling point, slight Coulomb friction produces a large dead zone around the stable and unstable equilibrium states of the pitchfork bifurcation in the case without Coulomb friction. Therefore, it is important in analyses of behavior of low-stiffness systems such as flexible structures used for spacecraft, to estimate the value of Coulomb friction at a supporting point. In this paper, we describe an experimental identification method for the bending moment attributable to Coulomb friction at the supporting points of a hinged-hinged beam. The moment attributable to dynamic friction is identified from experimental free oscillation by separating the effects of viscous damping and dynamic friction. For static friction, we use the equilibrium region in the bifurcation diagram because of static friction. In the vicinity of the buckling point, the region is very wide. Its boundary is obtained easily through experimentation. We describe a method for identification of the moment because of the static friction from the experimentally obtained boundary.

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This paper further investigates the Experimenta Wave Intensity Analysis (EWIA) method, which the authors proposed in a previous paper. EWIA combines experimental data (internal and coupling loss factors) with Wave Intensity Analysis (WIA). This paper analyses the characteristics of the coupling matrix of EWIA models and discusses how EWIA parameters affect the coupling matrix, and thus, the energy predictions. First, the construction of the coupling matrices of EWIA, WIA, SEA and ESEA are compared. Next, the analysis focuses on the non-direct coupling loss factors characteristic of WIA and EWIA formulations by presenting a physical interpretation and comparing them with the SEA and ESEA case. Finally, the matrix condition of the methods is compared and it is shown that the WIA and EWIA tend to have higher matrix condition numbers relative to the SEA and Experimental SEA. This indicates that the WIA and EWIA methods become more sensitive to matrix operations as the complexity and size of the system increases. This paper shows that the EWIA method preserves both the computational efficiency of WIA and the simplicity of its application respect to WIA, SEA and ESEA. As a result, EWIA works well without any additional effort compared to the SEA, WIA and Experimental SEA methods.

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The Transfer Influence Coefficient Method (TICM), which was developed by the authors, is effective in analyzing dynamic responses of structures. The TICM has the advantages of computational speed and accuracy compared with conventional methods. However, the TICM has not been available for the structures with closed loops, such as truss and rahmen structures. In this paper, a new algorithm of the TICM applicable to such truss and rahmen structures is presented. The algorithm presented here is provided for in-plane free vibration analyses of two-dimensional frame structures to aid in clarifying the fundamental procedure. The validity of the newly presented algorithm is demonstrated through some numerical computations. The present algorithm has a remarkable advantage in terms of computational speed compared with a conventional algorithm.

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