Because horizontal motion of a rotary crane generates undesirable two-dimensional load sway, skillful operators are needed to control the crane's motion; for this purpose, various types of control schemes have been proposed. Because natural frequency of the rope-load oscillation system affects the stability and performance of the control system, the controller design should consider robustness with respect to rope length. If the control system considers the effect of rope length variance, the crane's motion can be controlled without a sensor system for measuring it. This paper presents a control method based on linear matrix inequality optimization for achieving robustness with respect to rope length variance. Numerical simulations and experimental results demonstrate the effectiveness of the proposed method.

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Generally, both horizontal and vertical boom motion must be used to suppress the load sway caused by horizontal boom motion of a rotary crane. However, it would be less energy intensive and also safer if a control scheme could be developed that only used horizontal boom motion, i.e., without the need for any vertical boom motion. In addition, if load sway can be suppressed without measuring it, reduction in sensor cost can be achieved. Furthermore, employing simple velocity trajectory patterns such as trapezoidal and S-curve patterns, which are widely used in industrial automation systems, may provide cost effective controller implementation. This study presents a simple S-curve trajectory generation method for rotary crane motion that can suppress residual load sway using only horizontal boom motion without load sway sensing. Numerical simulations and experimental results demonstrate the effectiveness of the proposed method.

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A nutating sub-reflector is a convenient method for switching an antenna's beam between its target and background. Technically, the nutating mechanism introduces potential dynamical instability to an antenna structure. A typical nutator system can be roughly separated in two major rotating parts, the rocker and the reflector. Both of them equipped with controller, voice coil motor (VCM) and encoders/sensors. We propose combined dual plant modeling to reduce the couple system and combining the rocker and reflector plant in single transfer function form. Besides, the nutator system's stability, controllability and observability also are analyzed. Laser Doppler Vibrometer (LDV) and Dynamic Signal Analyzer (DSA) were used to experiment the realistic system and build up system dynamic response to verify the mathematical system. PID (Proportional-Integral Derivative) and PDFF (Pseudo-Derivative Feedback with Feed-forward Gain) were individually designed for it. Moreover, adding a white noise block in front of the VCM plant which can simulate the outside disturbance due to wind torque or other environmental impact. Our target was to proposed better effective control loop which inhibited the disturbance effectively. We present a complete analysis of combined dual plant modeling as well as control loop about the nutator system, and verifying the mathematical plant by LDV and DSA.

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Intersampling vibrations of a sampled-data positioning control system may lead to degrade the performance and reliability of mechatronic products. Such vibrations are caused by mechanical resonances with frequencies beyond the Nyquist frequency of the control system. To address this problem, we analyzed residual vibrations using a shock response spectrum (SRS) analysis employed for characterizing transient characteristics of mechanical resonances. We showed that the acceleration input in sampleddata control systems excited the mechanical resonance near the sampling frequency during a period of settling to a target position. These phenomena were confirmed through experiments using the actual head-positioning system of the hard disk drive. Consequently the vibrations caused by the mechanical resonances around the sampling frequency were not only the difficult to observe but readily excited by the control input. Therefore, the sampled-data positioning control system must be designed such that the sampling frequency is away from mechanical resonances.

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This paper is concerned with position control of asymmetric hydraulic cylinder system. The hydraulic system consists of an asymmetric hydraulic cylinder with two chambers connected by an orifice, a two-position, two-way proportional valve and a load force. The system structure and the control principle were introduced in this paper. The influence of some structural parameters on the system dynamic performance was analyzed. The analysis and simulation results indicate that a two-position, two-way proportional valve can achieve position control of the asymmetric hydraulic cylinder system. A good dynamic performance can be achieved after using the control strategy proposed by this paper.

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Magnetorheological fluids (MRF) are functional fluids which respond to an applied magnetic field with a change in rheological behavior. The objective of this study is to clarify an effective design method to develop the cylindrical MR fluid brake (cylindrical MRB). Before getting into the design, a testing cell to evaluate rheological properties of the MRF was developed. The experimental result was modeled as a characteristic curve which is independent of the shear rate. This model was utilized as fundamental data for design. A cylindrical MRB whose maximum torque is 10 Nm was also designed, and its braking torque was compared with the estimated torque with finite elemental method software for a magnetostatic analysis and proposed mathematical model of the MRF. Although the results show errors at off-state of the brake that come from a friction of an oil seal, the cylindrical MRB whose maximum torque is about 10 Nm was developed.

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A semi-active controller-based Fuzzy logic for a suspension system with magnetorheological (MR) dampers is presented and evaluated. An Inverse Fuzzy Model (IFM) is constructed to replicate the inverse dynamics of the MR damper. The typical control strategies are Linear Quadratic Regulator (LQR) and Linear Quadratic Gaussian (LQG) controllers with a Clipped optimal control algorithm, while inherent time-delay and non-linear properties of MR damper lie in these strategies. LQR part of LQG controller is also designed to produce the optimal control force. After that the LQG controller and the IFM models are linked to control strategy. The effectiveness of the IFM is illustrated and verified using simulated responses of a full-car model. The results demonstrate that by using the IFM model, the MR damper force can be commanded to follow closely the desirable optimal control force. The membership functions of IFM tuned by the results of Clipped optimal strategy. The results also show that the control system is effective and achieves better performance and less control effort than the optimal in improving the service life of the suspension system and the ride comfort of the car.

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In this paper, we analytically considered the effects of the in-plane stress of the disk on the changes of modal shape. The purpose of this study is to confirm whether the modal shape changes according to the in-plane stress. The results make it clear that the in-plane stress changes the modal shape and its curvature. The curvature of the modal shape is proportional to the reciprocal number of the bending stiffness. Thus, it is confirmed that the in-plane stress serves to change the bending stiffness distributions on the disk. Moreover, the natural frequencies of the disk are evaluated by two energy methods in which the variations of modal shapes are considered or not. The difference in the natural frequencies from two energy methods shows the effect of the changes in the modal shape of the disk due to the small difference in the results of the energy methods (maximum difference of strain energy: 7.1%). Finally, the two energy methods are compared to investigate the effects on the natural frequencies with hammering test. The experimental results show the traditional energy method is allowed to evaluate the natural frequencies practically.

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Among physical applications of a simple approximation of Bessel function of integer order can be referred to finding natural frequencies of the circular membrane using the novel method from the wave approach. In general, wave approach cannot be employed in the case of standing waves. This shortcoming can be removed by utilizing the idea of converting the standing-waves into moving-waves. By so doing, Bessel function which is a standing wave can be replaced by an exponential function. As a consequence of this conversion, it will be much easier to carry out variety of mathematical operation on the newly derived moving-wave in the form of exponential function. The results of present study evince that the solution obtained by this approach is so accurate and the same as those derived by using the cylindrical wave functions that will be investigated in this paper from wave approach. Of the important application of wave approach analysis is study of crack in mechanical systems. When we use the classical method for the systems having the crack, the relations will be complicate. This method can be applied to membrane which has discontinuities such as cracks, because the wave approach is convenient for these systems.

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Machine condition monitoring and diagnosis have become increasingly important, and the application of these processes to stationary structures and rotating machinery has been widely investigated. The authors previously proposed a stepwise diagnosis method. In that method, the location of the abnormality is first estimated using the force identification approach, and then the cause and the severity of the abnormality are identified. But the method was applicable for an abnormality of linear property. In this study, a stepwise diagnostic approach for a beam with an abnormality of nonlinear property, that is, a breathing crack, is proposed. In this method, the location and the severity of abnormality are identified by using the multi-frequencies of response under the abnormal condition. Using the numerical example of a uniform beam fixed at both ends, we confirmed the validity of the method and determined that the selection of the excitation frequency was very important. Moreover, we showed the applicability of the method by using experimental data. We conclude that the proposed diagnosis method is feasible for identifying the abnormality of a breathing crack.

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This paper proposes a new optimal control model of the human three-joint arm system (shoulder, elbow, and hand joints) and clarifies its basic performance. The proposed model is characterized by a freezing-like mechanism in its hand joint and optimizes its criterion function composed of three kinds of energy costs and a torque-change cost. The model's freezing-like mechanism is formulated as a feedback controller to produce feedback torque in the direction opposite to the hand-joint motion. Consequently, it was clarified that the minimization of the moment power of joints or that of the energy consumed by viscous resistance made it possible to simulate human three-joint arm's reaching movements including the hand-joint's freezing-like characteristics at the constant weight values regardless of target positions, whereas the torque-change minimization failed to do so. This result suggests that the energy minimization model with the freezing-like mechanism in its hand joint can be effective as a general and plausible model of the human three-joint arm control system and that the two kinds of energy can be involved in the trajectory planning for human three-joint arm's reaching movements.

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