In this paper, the authors present a possible model for a new type of damping structure (abbreviated to FPL) composed of a flexible porous material such as polyurethane foam and a liquid such as water. The model can be used to design the FPL so that it is suitable for various target vibrating objects. In a previous paper, the authors introduced the FPL and presented the damping effect of the FPL on the vibration of two types of specimens: a cantilever iron plate with a weight of 5.2 kg and a rail piece with a length of 1.2 m and a weight of 72 kg. Good damping performance of the FPL was shown in the paper. The FPL costs less than other viscoelastic materials, such as Sorbothane, and is anticipated to have a better damping effect. In addition, it was shown that the damping effect of the FPL depends on the properties of the liquid and porous material as well as the vibration characteristics of the target objects. Consequently, it is important to make a simple model of the FPL widely available for its design and engineering simulation. In this paper, the authors derive and propose a possible model of the FPL based on a simple dynamic and macroscopic perspective.

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In this study, the effects of prolonged exposure to whole-body vibration (WBV) on human physical response were investigated. In the experiments, the eight male subjects participated in a two hour driving simulation while being exposed to vertical random vibration. Five transmissibilities were obtained at thirty-minute intervals throughout the simulation. As the subjects viewed the driving simulation on a screen, they controlled the speed and direction with pedals and a steering wheel, respectively, although the vibration was stable and independent of the driving operation. Transmissibility was evaluated as the root-mean-square of transmissibility (T_rms), which was introduced to assess the amplitude of transmissibility within the frequency range of interest. The results showed that T_rms of the head transmissibility in the z-axis over time does not change significantly at the frequency range of interest (2-8 Hz) and that the change in T_rms depends on the test subject. However, when the magnitude of T_rms at the end of the two-hour driving simulation (“120 minutes”) is compared with that at the beginning (“0 minute”) in the same frequency band (2-8 Hz), T_rms tended to decrease over time. In particular, a significant difference between the two conditions was observed in the vicinity of the ±10% frequency range around the natural frequency. In addition, the changes in T_rms under conditions of with and without vibration were compared. Although the head transmissibility changed after exposure to WBV, the head transmissibility without vibration exposure showed no significant change.

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Human exposure to whole body vibration (WBV) affects the change of human sensory system such as discomfort and human fatigue. To investigate these cause-effect relationships, we examined if the human dynamic property changes due to with and without vibration. The aim of this study is to investigate the change of the seat-to-head transmissibility at two-hour intervals for “with vibration” condition, and compared the results with those obtained for “without vibration” condition. A preliminary study explored the change of seat-to-head transmissibility at two-hour intervals, in which the subjects were not exposed to whole-body vibration. In this study, eight male subjects performed a car driving simulation while exposed to vertical vibration for two hours. Transmissibilities were measured once before and once immediately after the driving simulation. While they played the driving simulation on a screen, they were exposed to vertical random vibration (0.2-0.3 m/s² in r.m.s.) in the 1-30Hz frequency range. The transmissibility was evaluated in the root-mean-square value (T_rms), which is introduced in order to assess the amplitude of transmissibility within the frequency range of interest (2-20 Hz). The results show that T_rms of “after” two-hour driving for “with vibration” appear to become smaller than that of “before” driving. On the other hand, when T_rms's of “before” and “after” were compared for “without vibration”, no significant difference was observed. Moreover, by comparing the distribution of damping ratio for “with vibration” with that for “without vibration”, no significant difference appeared.

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This paper proposes design of end-effector and prototype of thermal cutting system for harvesting sweet peppers. The design consists of two parallel gripper bars mounted on a frame connected by specially designed notch plate and operated by servo motor. Based on voltage and current, two different types of thermal cutting system prototypes; electric arc and temperature arc respectively were developed and tested for performance. In electric arc, a special electric device was developed to obtain high voltage to perform cutting operation. At higher voltage, electrodes generate thermal arc which helps to cut stem of sweet pepper. In temperature arc, nichrome wire was mounted between two electrodes and current was provided directly to electrodes which results in generation of high temperature arc between two electrodes that help to perform cutting operation. In both prototypes, diameters of basic elements were varied and the effect of this variation on cutting operation was investigated. The temperature arc thermal system was found significantly suitable for cutting operation than electric arc thermal system. In temperature arc thermal cutting system, 0.5 mm nichrome wire shows significant results by accomplishing harvesting operation in 1.5 seconds. Also, thermal cutting system found suitable to increase shelf life of fruits by avoiding virus and fungal transformation during cutting process and sealing the fruit stem. The harvested sweet peppers by thermal cutting system can be preserved at normal room temperature for more than 15 days without any contamination.

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The gyroscopic exercise tool to train the hand muscle, which utilizes the gyroscopic effect caused by the whirling motion of the high speed rotating body is considered. This tool shows the contact phenomenon between the rotor and the case. When the input motion with several Hz is added to the case, the rotor spins in thousands rpm whirling with the slow precession motion. Conventional studies on this tool have assumed the continuous rolling motion of the rotor on the track in the case. This paper does not set this assumption, and develops the dynamical model of this tool considering the contact/separation conditions and the slide between the rotor and the case. Two kinds of motions are observed in the numerical simulation, one is the uniform precession synchronous to the input case motion which was observed in the conventional studies. The other is the periodically reverse precession asynchronous to the input motion, which was not observed in the conventional studies. These two motions are physically explained, their stabilities are clarified by the energy analysis. These motions are also observed in the experiment.

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Operations of hydraulic excavators require high operation skill and operators have possibilities to work in unsafe environment. To solve these problems, automatic digging control is often studied, but there are few studies focused on improvement of efficiency. A high efficiency digging algorithm for a hydraulic excavator has not been established because relationship between digging motion and digging performance is very complex. A simulation model which is able to consider interaction between soil and machine would help to establish a digging algorithm for improving energetic efficiency. In this paper, an example for improvement of digging efficiency is shown by our developed distinct element method (DEM) simulation. First, in order to improve the accuracy of the DEM simulation, the parameter identification test is carried out to identify damping ratio and friction coefficient between soil particles. Besides, accuracy of digging efficiency evaluation by the developed simulation is shown by a developed digging test device which can reproduces excavation by hydraulic excavator. Finally, digging simulations are conducted by our suggested automatic digging algorithm. Varying control parameters, the simulation estimates influences of control parameters. These simulation results show that the simulation is able to specified control parameters which improve digging efficiency. Our research evaluates effectiveness of model-based development for automatic digging which enhances efficiency.

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