The dynamic processes of a flexible manipulator consist of flexible and rigid motion components. The dynamic equations expressing the motion can be divided into two corresponding subsets, and a decomposed dynamic control (DDC) is proposed for the design of a controller for a flexible manipulator. The DDC is composed of flexible dynamic control and rigid dynamic control: the flexible dynamic control involves developing a desired trajectory through considerations of the physical properties of the device based on a feed-forward strategy; the rigid dynamic control aims at tracking the desired trajectory based on a feedback strategy. This report mainly investigates the flexible dynamic control which searches for a desired trajectory considering nonlinearity. An optimization method applying the Nelder-Mead simplex (NM) algorithm is proposed to obtain the desired trajectory. Numerical simulation and experimental results show that the optimization can deal with the extremely nonlinear problems. Additionally, the conclusion that optimization is strongly dependent on the accuracy of the model is possible, for further research, a more robust controller will be investigated.

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In this study, a nonlinear attitude controller for a small unmanned electric helicopter is designed by using quaternion feedback provided by the backstepping control method. First, a quaternion-based multi-input multi-output(MIMO) nonlinear attitude model of a small helicopter is derived. This nonlinear model consists of three parts, namely, the time derivatives of the quaternion, the Euler equation of rotation, and the flapping dynamics of the main rotor and the stabilizer bar. Next, a nonlinear MIMO controller that calculates the desired torque input by the backstepping control method is designed. The control law is modified to exclude a online computation of time derivatives of sensor output. The controller achieves the asymptotic stability of the origin of the attitude error system, and guarantees that the helicopter could track arbitrary desired attitude. Finally, a simulation and experiment are performed, and the results of this simulation and experiment show the effectiveness of the suggested nonlinear MIMO controller.

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In this paper, we examine the parameterization of all stabilizing multi-period repetitive controllers for single-input/single-output time-delay plants with the specified input-output characteristic. The parameterization is the problem to find all stabilizing controllers. The parameterization of all stabilizing multi-period repetitive controllers for non-minimum-phase plants and that of all stabilizing multi-period repetitive controllers for time-delay plants were solved by Yamada and Satoh. However, using the method by Yamada and Satoh, we cannot settle input-output characteristics easily. Because the input-output characteristic is related to four free parameters. If the parameterization of all stabilizing multi-period repetitive controllers with the specified input-output characteristic, which is the parameterization when low-pass filters are settled beforehand, is obtained, we can specify the input-output characteristic easily. In this paper, we propose the parameterization of all stabilizing multi-period repetitive controllers for time-delay plants with the specified input-output characteristic.

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In this study, we apply an anti-windup scheme to the vehicle active suspension system. A fixed-order output feedback controller which does not explicitly take into account the actuator saturation constraint is first designed. Then, an anti-windup compensator is designed to handle the saturation constraint. Local control design technique based on the circle criterion and L₂ gain performance is used for the anti-windup compensator synthesis. A quarter car model is considered in this study and the effectiveness of the proposed approach is shown by a numerical example.

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In recent years, it has been reported that the dynamics and sensibilities of passengers differ from a driver. However, there has been little research on the control of suspension that takes into consideration the dynamics of the human body and its sitting position. In this paper, semi-active suspension control is developed to reduce passenger’s vibration and motion. First, a vehicle and passenger model including the dynamics of human body and the sitting position is constructed. Second, robust control system design method which uses the vertical acceleration of a passenger’s head as one of the controlled output, is proposed. In order to control the jerk which is generated by changing of a damping coefficient rapidly, the robust controller is designed based on the Lissajous figure of damping force. From the result, it was confirmed that at nearly the resonance frequency of the vertical direction of the passenger’s head, the proposed control method can reduce the passenger's vibration better than general methods of control that use a vertical acceleration of the vehicle body as one of the controlled output.

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This paper deals with the motion of a submerged tethered system subject to large deformations and displacements. A tethered system usually employs a cable or wire rope to tether an attached piece of equipment to the ground or to a vehicle, e.g., a remotely operated vehicle (ROV) in the sea. The motion of a tether was modeled using the Absolute Nodal Coordinate Formulation in which absolute slope of elements are defined as nodal coordinates. Herein, this formulation is adapted to account for hydrodynamic drag, buoyancy and added mass. By using the slope coordinates, the hydrodynamic drag acting on the curved shape of the deformed elements can be accurately calculated. Three kinds of experiment were conducted into the fundamental motion of the submerged tether when subject to large deformations and displacements. The numerical results from the proposed model agreed well with the experimental results.

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In this study, a new diagnosis approach for a beam structure is proposed to increase the robustness of the stepwise primary diagnosis method. The distinguishing feature of this method is that the mathematical model is modified based on the difference of the response between the measurement and the simulation. To this end, the response ratio is defined between the measured and simulated response under the normal condition, and the mathematical model is modified by using the response ratio to adjust it to the measured property. Using the random excitation test, we can identify the location of abnormality at various excitation frequencies and obtain the final result of the abnormal location based on its mean value with a standard deviation. We checked the feasibility of the proposed method using the experimental data of a free-free uniform beam excited at the center. An additional mass was considered as an example of abnormality. As a result, the location and the cause of abnormality can be identified for five levels of abnormality by using the proposed method. The results indicate that the proposed method is a feasible way to diagnose the practical structure of a beam.

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Modal differential sub-structure method which can quickly predict effects of structural modifications has been proposed by the authors. This method is a kind of component modal synthesis and utilizes dynamic current characteristics of modification structure. The method is convenient because it does not require the user to determine the structure modification segmentation beforehand and the user can choose it after checking dynamic characteristics of current structure. This paper elucidates the difference of formulation between the proposed method and conventional methods. As with other component modal synthesis methods, however, the predictions of effects of structural modifications with this method involve errors. In this paper, a technique to reduce those errors is proposed and the method is compared with conventional methods in terms of error reduction effect and computational efficiency.

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In order to properly evaluate the effect of tensioning on a circular saw, it is essential to use the change in the natural frequency of the saw blade when tensioning. This paper presents a spatial filter called a modal filter to easily measure the natural frequencies for only the modes necessary for the evaluation of the tensioning effect. The modes necessary for the evaluation are indicated based on the backward traveling wave frequencies of a rotating circular saw, which are calculated using the finite element method. The modal filter is designed based on the mode shapes of a disk. The examples show that the natural frequencies for the modes with nodal diameter numbers 0, 1 and 2 are necessary for the evaluation of the tensioning effect. The information on the nodal diameters of a disk enables us to easily design proper sensor locations for the modal filter for a disk such as a circular saw. The modal filter designed extracts separately the three modes necessary for the evaluation.

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A design basis ground motion is usually defined to be compatible with a given response spectrum which is a useful measure of linear dynamic response of a structure. It has been known that the variance of maximum displacement responses to artificial ground motions in elasto-plasric region is quite large, although every artificial ground motion fits the same design response spectrum. Recently, a new synthesis method was proposed by Masuda, et al. that can generate artificial earthquake ground motions compatible with given time-frequency characteristic as well as a given response spectrum. In this paper, a group of artificial earthquake ground motions are generated, and elasto-plastic response analyses are carried out to examine variance of structural responses in elasto-plastic region. It is revealed that the variance of the structural responses to the earthquake ground motions generated by Masuda's method is less than that to the seismic ground motions by the conventional design method. And it is suggested that the given time-frequency characteristic has an effect on the variance of maximum responses.

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This paper deals with an experimental study on flow-induced waves generated on a thin film under shear loading subjected to a fluid flow in a narrow passage. The experiment is carried out to investigate the deformed shape of the thin film with various values of shear loading, and the vibration characteristics of the flow-induced wave generated on the thin film. As a result, it is clarified that the flow-induced wave occurs to the thin film caused by the propagation of corrugation due to the fluid flow in the narrow passage. The critical flow velocity of the flow-induced wave drastically decreases caused by the generation of corrugation on the thin film due to the shear loading. Moreover, it is clarified that the traveling direction of the flow-induced wave is determined by the deformed shape of corrugation and fluid flow direction. The flow-induced wave propagates diagonally, almost across the fluid flow direction.

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The self-excited whirl of an axially symmetric cylinder mounted on an elastic support system and partially filled with liquid is analyzed. Rotor unbalance, gravity, and gyroscopic terms are considered to be negligible. The whirling motion is assumed to be parallel to the axis and the liquid motion is taken as being axially uniform. In the analysis, under the assumption of a thin liquid layer, the shallow-water theory is applied to basic equations to more easily incorporate nonlinearities that exist in the surface wave of a liquid in a rotor. Applying the Galerkin method to the equations based on the shallow-water theory obtains the modal coupling equations. The harmonic balance method is applied to the modal coupling equations to obtain periodic solutions. The analytical whirl amplitudes are in good agreement with the experimental ones in previous studies under large external damping ratios. The time series analysis based on the modal coupling equations reproduces the periodic and aperiodic amplitude modulations observed in the experiment.

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