To date, most passive walkers have been designed with arc-shaped feet rigidly attached to the legs. However, the friction torque against yaw is often insufficient because of their contact conditions with the ground. We developed a simple 3D straight-legged passive walker with flat feet and ankle springs. Flat feet were used to gain enough scrubbing friction to oppose unstable yaw motion. Springs were attached to the ankle to produce torque resulting in roll and pitch motions that mimic those of 3D passive walkers with arc-shaped feet, while the friction torque against yaw should be sufficient. The spring constant for the roll motion at the stance ankle is obviously an important factor in enabling the straight-legged robot to rock adequately from side to side to avoid problematic scuffing of the swing leg so it can swing forward. We used numerical simulations to determine the value of the spring constant. Experimental results indicated that our 3D straight-legged passive walker with a 0.77-m leg can walk more than 2 m at about 0.46 m/s.

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In this paper, a robotic boat model of combined yaw and roll rate is obtained by a system identification approach. The identified system is designed with frequency-shaped sliding mode control. The control scheme is composed of a sliding mode observer and a sliding mode controller. The stability and reachability of the switching function are proved by Lyapunov theory. Computer simulations and experiment carried out at INAGE offshore show that successful course keeping and roll reduction results are achieved.

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In a CNC Video Measuring System, both very-low-speed motion and high-speed motion are required. Very-low-speed motion is highly influenced by friction. Currently, PID control with look-up-table gains is used to handle with this problem. However, the process of developing this table tends to be a trial-and-error scheme. In the present paper, we investigate a model-based control system design. System identification techniques are used for constructing a model for a control system design and a sliding mode controller with a frequency-shaped hyperplane is designed using that model. Both strong attenuation of disturbances at low frequencies and stability at high frequencies are achieved in a real machine.

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This paper presents a technique to cope with undesirable frictional effects in positioning control of a pneumatic actuator. This technique is based on an observer for estimating the dynamically varying friction force on-line. The observer is derived from an available nonlinear observer for Coulomb friction by modifying it to fit the pneumatic actuator and to enhance its estimation ability. Our pneumatic servo system for positioning consists of an inner pressure control loop, an outer position control loop, the friction observer, and a velocity observer. In this system, the friction force is compensated by adjusting a desired pressure value sent from the outer loop to the inner loop according to the friction observer output. Experimental comparisons with a conventional control system using friction compensation by means of accelerometer information feedback were carried out and show that our system works with almost the same high positioning accuracy as the conventional system, despite having neither an accelerometer nor a velocity sensor, and is more advantageous from the perspective of cost performance.

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This study analyzes the skill component of the wrist release in the golf swing by employing a three-dimensional dynamic model considering vibration of the club shaft. It is observed that professional and expert golfers relax their wrists in the swing motion as a "natural" or "late" release. Thus, the relationship between the timing of the wrist release and the shaft vibration is examined in this study. First, it is demonstrated that "natural release" at the zero-crossing point of the bending vibration of the shaft efficiently increases the head speed at impact. In the next step, the "late hitting" condition is imposed upon the model. It is demonstrated that "late hitting" could further improve the efficiency of the swing motion. Finally, the skill component in the wrist release for the long drive is experimentally verified by measuring the movement of the wrist and the dynamic deformation of the shaft during the downswing.

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In this study, the optimal seismic design methodology that can consider the structural integrity of not only the piping systems but also elasto-plastic supporting devices is developed. This methodology employs a genetic algorithm and can search the optimal conditions such as the supporting location, capacity and stiffness of the supporting devices. Here, a lead extrusion damper is treated as a typical elasto-plastic damper. Four types of evaluation functions are considered. It is found that the proposed optimal seismic design methodology is very effective and can be applied to the actual seismic design for piping systems supported by elasto-plastic dampers. The effectiveness of the evaluation functions is also clarified.

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We created periodically varying waveforms, which are rectangular, trapezoidal, triangular, and quasi-sinusoidal waveforms, by using the originally presented equations and we have investigated the effect of waveform on the frequency characteristics by FFT analysis. Under a excitation vibration having a symmetric quasi-sinusoidal waveform, the fundamental frequency of the system and frequencies at its odd numbered cycles appear. The fundamental frequency of the system and its integral-multiple frequencies appear under excitation vibration having an asymmetric quasi-sinusoidal waveform with the peaks shifted to right or left. Under vibration having a quasi-sinusoidal waveform, an angular frequency of 1 appears in addition to the excitation frequency when damping terms are not included, but it does not appear when damping terms are included.

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An algorithm was developed for identifying and tracking natural vibration modes. Its main feature is the using of image operations. This enables the pattern recognition of natural vibration modes and the automatic surveying of parameters in vibration design even when the change of order in which natural vibration modes appear occurs. The developed algorithm consists of the following steps. First, the absolute value of each component of a vector corresponding to a natural vibration mode is represented as a gray-scale image of each component by a computer post processor. Each of the gray-scale images is then binarized with white and black colors. The numbers of the groups consisting of pixels with the same color are counted in each binary image, and the numbers are used for distinguishing natural vibration modes that should be tracked from the others. A structural optimization system was developed that contains a software routine using the developed algorithm. The reliability of the developed algorithm was examined through some calculation examples.

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Vibration modes of an extremely thin rotating circular membrane subjected to transverse distributed load are investigated. In the previous paper, the author proposed an analytical method to obtain equilibrium states with large transverse deformations employing the von Karman theory and taking account of buckling under the assumptions of rotationally symmetric deformations. In this paper, transverse vibration equation around the equilibrium state under transverse load is derived and modal equation is formulated. The equation is numerically solved and modal frequencies and modal shapes are obtained. Typical vibration modes are illustrated. In order to confirm the validity of the analysis, eigenvalue analysis of a spring-mass system model for the membrane are performed to obtain vibration modes. A fairly good agreement is found between the theoretical and numerical results. Experiments of thin rotating circular membranes under gravity in vacuum are also conducted and transverse vibration frequencies are measured for a variety of rotation speed and air pressure. Analytical results are compared with the experimental results to verify the validity of the present analysis.

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This paper studies the dynamic response of a rotating multi-span shaft with elastic bearings subjected to an axially moving load. The moving load is motivated by the cutting forces in machining process. The multi-span shaft with elastic bearings models a system that a rotating shaft is mounted by the tailstock and chuck and the steady rests are installed between the ends of shaft. The tailstock and steady rest are modeled as the translational springs and the chuck is assumed as the combination of the translational and rotational springs. The system equations of motion are derived based on the global assumed mode method. The numerical results are obtained to examine the effects of the moving speed of the load, the rotational speed of the shaft, the number of spans, and the stiffnesses of the translational and rotational springs. The numerical results show that the deflection of shaft under the moving load significantly decreases due to the intermediate supports. Moreover, the dynamic behaviors of shaft will be similar when the stiffness of translational spring exceeds the critical stiffness value.

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Nonlinear vibrations of elastic structures containing two cylindrical liquid-filled tanks subjected to vertical harmonic excitation are investigated. When a 2:1:1 ratio of internal resonance is satisfied between the natural frequencies of the structure and the sloshing in the two liquid tanks, nonlinear parametric vibrations can be observed. The equation of motion for the structure is derived considering the nonlinearity of the hydrodynamic force, and the modal equations for sloshing are derived by using Galerkin's method. Then, frequency response curves are determined by using van der Pol's method. The respective influences of the liquid levels and the deviation of the internal resonance ratio 2:1:1 on the frequency response curves are discussed. The results of the response curves differed from those obtained in the case where a structure had only one liquid-filled tank installed. It is found that two types of vibrations may occur depending on the excitation frequency and the liquid levels: a single-mode solution (sloshing occurs in either tank) and a double-mode solution (sloshing occurs in both tanks). Amplitude and phase modulated motion appears in the single-mode solution when some deviation of the internal resonance ratio exists. The validity of the theoretical results was verified by the experiments.

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This paper proposes an optimum design method of journal bearing for minimizing the total life cost which includes not only the initial cost but also the running cost. Journal bearing is one of the typical friction part and physically severe part in machine elements. Therefore, maintenance is required to prevent failure and to keep performance. For this object, the running cost by the maintenance is user's burden. Thus, the optimum design method of the bearing for minimization of the total life cost is required. In this research, the evaluation functions of the total life cost which contains the initial cost and the running cost of the bearing are discussed and the optimum design is proposed under the physical constrain, that is Thermo Hydrodynamic Lubrication theory (THL theory), and inequality constraints. Then design valuables of the optimum journal bearing are obtained.

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Bolted joints are widely used in mechanical structures as they allow easy disassembly for maintenance without high cost. However, vibration-induced loosening due to dynamic loading remains a long-unresolved issue. We have developed a new type of nut named the hyper lock nut (HLN) that offers anti-loosening performance without a complicated tightening process and tools. In this study, we investigated the mechanisms of joints bolted with the HLN, and tightening behavior was analyzed using the three-dimensional finite element method. The analytical results were compared with the experimental results for the HLN, and close qualitative agreement was observed between the two with respect to displacement, tightening force and tightening torque. We found a number of new aspects and plus points for joints bolted with the HLN in comparison to those fastened with JIS standard nuts. It was found that the tightening torque of the HLN is higher than that of JIS standard nuts, and that satisfactory anti-loosening performance can be realized through the thread contact force at the slit region and the angular face of the bearing surface.

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