Research on multibody dynamics in engineering and science is developing at a high pace in Japan and in the world. These activities provide efficient and powerful solution tools for solving complicated dynamic problems with control via theoretical or high performance in-house and/or general purpose computer programs in academic and industrial fields. Thus, advancement of research is an important index for measuring competitiveness in education and industry in terms of “dynamics and control”. The aim of this paper is to present an overview of the various research activities of multibody dynamics in Japan.

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This paper describes a vision-based tracking system using an autonomous Quadrotor Unmanned Micro-Aerial Vehicle (MAV). The vision-based control system relies on color target detection and tracking algorithm using integral image, Kalman filters for relative pose estimation, and a nonlinear controller for the MAV stabilization and guidance. The vision algorithm relies on information from a single onboard camera. An arbitrary target can be selected in real-time from the ground control station, thereby outperforming template and learning-based approaches. Experimental results obtained from outdoor flight tests, showed that the vision-control system enabled the MAV to track and hover above the target as long as the battery is available. The target does not need to be pre-learned, or a template for detection. The results from image processing are sent to navigate a non-linear controller designed for the MAV by the researchers in our group.

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On ground stereo vision system is used for autonomous hovering and landing of a quadrotor Micro Aerial Vehicle (MAV). This kind of system has an advantage to support embedded vision system for autonomous hovering and landing, since an embedded vision system occasionally gives inaccurate distance calculation due to either vibration problem or unknown geometry of the landing target. Color based object tracking by using Continuously Adaptive Mean Shift (CAMSHIFT) algorithm was examined. Nonlinear model of quad-rotor MAV and a PID controller were used for autonomous hovering and landing. The result shows that the Camshift based object tracking algorithm has good performance. Additionally, the comparison between the stereo vision system based and GPS based autonomous hovering of a quad-rotor MAV shows that stereo vision system has better performance. The accuracy of the stereo vision system is about 1 meter in the longitudinal and lateral direction when the quad-rotor flies in 6 meters of altitude. In the same experimental condition, the GPS based system accuracy is about 3 meters. Additionally, experiment on autonomous landing gives a reliable result.

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Swashplate mechanism is the steering control mechanism, used in most helicopters. It is a complex multi-loop closed kinematic chain which controls the angles of attack of the main rotor blades. In most new model helicopters, this mechanism is also equipped with the bell-hiller stabilizer bar (flybar), to improve the stability. The main purpose of this paper is the dynamic analysis of a swashplate mechanism, one of the latest architectures, used for hingeless rotor with the flybar. The underlying kinematics has been discussed in Part I. Thus, the detailed dynamic analysis of the whole mechanism and each part are presented here. The analyses are based on the parallel manipulators concept and the virtual work principle. Also an ADAMS rigid body dynamic model was developed to verify the results of the analytical model. In many simulated cases, the results matched.

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This paper proposes a method for interpreting fuzzy linguistic information by acquiring robot's experience on previous movements. The quantitative assessment for a fuzzy linguistic term such as “little” depends on the spatial arrangement of surrounding environment. Robot's experience on previous movements is very useful for understanding such information in a context dependant manner. Therefore, an internal rehearsal system is introduced to acquire the robot's experience on previous movements. Such acquisition enhances the robot's capability to interpret fuzzy linguistic information in fuzzy voice commands (FVCs) according to the current environmental context. The proposed system is used to evaluate the fuzzy linguistic information related to primitive movements of a robot manipulator. Those primitive movements are realized by a behavior evaluation network (BEN) with the guidance of an internal rehearsal system. The end-effector movements and the single joint movements of a robot manipulator are considered as primitive movements. They are activated by fuzzy voice motion commands (FVMCs) and fuzzy voice joint commands (FVJCs) respectively. The proposed idea is demonstrated with a PA-10 robot manipulator by navigating the robot manipulator in the user's working space. The use of the behavior evaluation network and the internal rehearsal system introduced a better way of assessing fuzzy linguistic information by acquiring the robot's experience on the corresponding environment.

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This paper deals with the problem of designing a controller for multirate sampled systems with slow output sampling and fast input updating rates. An adaptive output estimator based on a reduced first order model of the controlled system will be proposed in order to design an output feedback controller with a fast-rate input updating period. The proposed adaptive output estimator is designed for a reduced first order model of the controlled system and so has relatively simple structure compared with common adaptive observers. The results reported here are validated on an experimental liquid level process system.

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The lightweight racket with handle-light configuration and large head size is recent tendency of high-tech tennis rackets, increasing power or post-impact ball velocity with an increasing racket swing speed. This paper investigated the performance of lightweight tennis racket with super-large head size in terms of feel or comfort. It predicted the effect of the mass and mass distribution of super-large sized rackets on the impact shock vibrations of the racket handle and the player's wrist joint when a player hits a flat forehand drive. The prediction is based on the identification of the racket characteristics, the damping of the racket-arm system, equivalent mass of the player's arm system and the approximate nonlinear impact analysis in tennis. A super-light weight balanced racket (mass: 292 g, the center of gravity L_G: 363 mm from the butt end) and a conventional weight and weight balanced racket (349 g, L_G: 323 mm) are selected as representatives. They are the super-large sized rackets made of carbon graphite with a head size of 120 square inches and the same geometry. The result showed that the shock vibration of the super-light weight balanced racket with super-large sized head is much larger than that of the conventional weight balanced type racket. It also showed that the sweet area of the former in terms of the shock vibration shifts from the center to the topside on the racket face compared to the latter. This is because the location of the grip on the racket handle is further from the location of the node on the handle of the first mode of super-light racket than that of the conventional weight racket.

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In this study, the applicability of a previously developed optimal seismic design methodology, which can consider the structural integrity of not only piping systems but also elasto-plastic supporting devices, is studied for seismic waves with various frequency characteristics. This methodology employs a genetic algorithm and can search the optimal conditions such as the supporting location and the capacity and stiffness of the supporting devices. Here, a lead extrusion damper is treated as a typical elasto-plastic damper. Numerical simulations are performed using a simple piping system model. As a result, it is shown that the proposed optimal seismic design methodology is applicable to the seismic design of piping systems subjected to seismic waves with various frequency characteristics. The mechanism of optimization is also clarified.

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We presented a vibration system that has a horizontally asymmetric restoring force as a result of attaching a spring perpendicularly to the direction of vibration and imparting the guide way of the oscillator with an angle relative to the direction of vibration. And we have investigated the chaotic characteristics of the system by performing numerical calculations. The purpose of this study is to clarify the vibration characteristics and to contribute to the creation of devices for generating nonlinear chaotic vibrations. From the analytical results, it was found that imparting an angle to the guide way facilitates the transition of the system vibrations to chaos. Transition to chaotic vibrations occurs more easily when the excitation amplitude is smaller than the natural length of the spring and when the spring is initially compressed. However, chaotic vibrations occur even when the spring is initially tense when an angle is imparted to the guide way.

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Continuous operation of rotating machinery with a rotor crack is a risk condition since the rotor crack grows rapidly and may fail causing a catastrophic accident. This paper develops the finite element model of the rotating shaft with an open crack. The analytical method for the calculation of the natural frequencies of such a rotor system with an open crack is investigated, and the modeling of the open crack element is discussed. The natural frequency of the experimental system is measured for various cases of positions and depths of the open crack. By comparing both the theoretical and experimental results of the natural frequencies, the accuracy of the developed finite element model of the rotating shaft with an open crack is clarified.

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The squeal phenomenon is often generated in bicycle disc brakes. This paper deals analytically with the generation mechanism and the criterion of whether or not the squeal occurs. According to the experimental studies, it has been made clear that the squeal is mainly in-plane vibration in the direction of disc surface with the frequency about 1kHz caused by frictional characteristics with negative slope with respect to the relative velocity. An analytical model of the bicycle disc brake system has been devised to confirm the experimental results, in which a coupled in-plane and out-of-plane vibrating system is composed of the disc, hub, caliper and spokes. The resulting frequency of squeal and the unstable vibration modes of the disc and spokes from the analytical model agreed well with the experimental results.

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