This paper describes a novel design concept for a tool for cutting carbon-fiber-reinforced plastic (CFRP) composites. The cutting tool, which is termed a two-layer tool, was fabricated from two materials with a spatial distribution of hardness around the tool edge. In the two-layer tool, the rake face is made of a material with a relatively high wear resistance, i.e., polycrystalline diamond (PCD), whereas the flank face is made of a material with a relatively low wear resistance, i.e., tungsten carbide (WC-Co). The results of milling tests conducted with a unidirectional CFRP laminate and the two-layer tool showed that the existence of a hardness distribution works to reduce cutting forces, because the wear process of the two-layer tool develops with a constant roundness at the tool edge over relatively long cutting distances. A simplified model was developed to describe how friction force is reduced. Increasing the difference between the wear resistances of the PCD layer and the WC-Co substrate and increasing the clearance angle of the tool edge were found to be effective in reducing the cutting forces. The finding of this study will be helpful in the development of novel design concepts for extending the life of tools for cutting CFRP composites.
High-speed cutting has various advantages such as high material removal rates and reduction of machining time. However, the greatest problem of high-speed cutting is its excessive tool wear rate. This is attributed to the fact that high-speed cutting causes a large cutting temperature rise and then, promotes the occurrence of tool material diffusion. In this study, we focused on extremely short-duration cutting. If the cutting duration for each edge undergoing the intermittent cutting process is designed to be considerably smaller than the time constant of thermal diffusion, the temperature rise at a tool face can be suppressed to a low value; i.e., the diffusion wear due to temperature can be reduced. In this method, since the cutting volume of a single pass is small, in order to cover the total cutting volume as in is the case of ordinal cutting, the number of cutting cycles is increased. Thus, mechanical wear will increase with a shortening of the cutting period. Therefore, to reduce the total wear volume in extremely short-duration cutting, we need to design tool edge geometries that can lessen mechanical wear and investigate the optimum cutting period in which the tool wear can be minimized. In this study, we investigated the effect of the tool rake angle and the inclination angle on the wear volume. Then, we measured the tool temperature and the wear volume for various cutting periods during a single pass and at different cutting speeds. Consequently, we found that the smaller the cutting duration, the smaller are the temperature rise at the flank face and the tool flank wear. Several experiments suggested that extremely short-duration cutting has a high potential for achieving high-efficiency metal removal.
For maintenance microrobots for small diameter pipes in power plants and so on, a novel microgripper using divided-electrode type flexible electro-rheological valves (DE-FERVs) was proposed and developed. Each bendable finger consisted of the DE-FERV and a hydraulic rubber actuator and was several millimeters long. The DE-FERV had an axially divided parallel plate electrode pairs in a flexible tube. Each parallel plate electrode pair controlled the electro-rheological fluid (ERF) flow by changing the viscosity with the electric field. The DE-FERV had both high flexibility and sufficient pressure control range. The hydraulic rubber actuator had plural integrated walls inside to restrict its radial expansion and axially extended by the inner pressure controlled by the DE-FERV. A finger large model was fabricated and experimentally characterized. Then, a gripper having two fingers was constructed and the object handling was demonstrated.
An electro-conjugate fluid (ECF) is a dielectric liquid generating powerful flow when high DC voltage is applied with electrodes inserted. The ECF flow is generally known as a kind of electrohydrodynamics phenomenon. Although the ECF flow is applicable for attractive applications, its prediction by numerical simulation, which could be a powerful tool for optimum design, has been far from satisfactory. One of the plausible reasons for this failure is insufficient consideration of the electric double layer (EDL), in which positive and negative charges are stratified on the electrode surface. This study first confirms the presence of EDL by measuring the potential distribution between the symmetrical pole electrodes (φ0.3-mm stainless steel wires) inserted in the ECF. Subsequently, the ECF flow simulation is performed by taking into account the EDL. The governing equations of ECF flow consist of a modified Poisson-Boltzmann equation, the charge conservation with charge recombination, the Korteweg-Helmholtz equation, the continuity equation and the incompressible Navier-Stokes equation. These governing equations give the distribution of potential, electric field, charge density and flow velocity as a result of numerical computations. We demonstrate that by properly considering the EDL the numerical simulation can reasonably well reproduce the ECF flow in terms of the velocity distribution and the induced flow rate.
High-performance lubricating additives are desired in order to improve the properties of lubricating fluids. Recently, carbon nanomaterials such as fullerenes, carbon nanotubes, and carbon onions have been studied as lubricating additives for water and lubricating oils. However, the costs of these carbon nanomaterials are too high for practical use. On the other hand, graphene oxide (GO) is a carbon nanomaterial that consists of single atom thick sheets that possess a large number of oxygen functional groups. Since GO is synthesized from graphite using a chemical liquid process, the cost of GO is significantly lower than other carbon nanomaterials. In this study, the application and tribological properties of GO monolayer sheets as additives in water and poly-alpha olefin (PAO) were investigated. The dependence of the friction coefficient of GO-water dispersions on GO concentration (0.01-1.0 mass %) was investigated. In particular, GO-water dispersions with a concentration of less than 0.1 mass % demonstrated low friction coefficients. In this study, GO was simply dispersed in PAO using surfactant and intermediary solvents without the need for drying treatments. We found that the use of anionic surfactants in the GO-PAO dispersions was better than cationic surfactants in terms of the degree of wear observed. Specifically, GO-PAO dispersions that used an anionic surfactant with a GO concentration of 4 mass % had the smallest wear in this study. Moreover, friction coefficients were not decreased by the addition of GO in PAO. Finally, we found that intermediary solvents did not affect lubrication.
Hydraulic systems have high-power density because its oil transmitting power has high rigidity. However, when air bubbles are mixed into oil, they reduce oil stiffness and decrease system efficiency. This study mitigates this problem by removing air bubbles from the oil using an active bubble elimination device that uses a swirl flow to eliminate air bubbles from a hydraulic fluid. We focus on the relationship between the change in the bulk modulus and elimination of air bubbles from the hydraulic fluid and experimentally measure the bulk modulus of the hydraulic oil with and without air bubbles. Moreover, to clarify the relationship between the amount of air bubbles and the effective bulk modulus of oil, we propose a mathematical model of the bulk modulus of oil containing air bubbles. The experimental results indicate that the effective bulk modulus of oil increases by eliminating the air bubbles in oil, and the curve of the bulk modulus with the bubble eliminator turned off has a small hysteresis depending on whether it is pressurized or depressurized. We investigate the calculation method of the effective bulk modulus by considering the amount of air bubbles and the amount of air being dissolved and released. Finally, we confirm that the effective bulk modulus calculated using the mathematical model agrees well with the experimental results. We conclude that the volume of air contained in the oil and the differences due to the process of dissolving and releasing air significantly influence the bulk modulus of the hydraulic fluid.
This report discusses relationship between a handle rotational feeling in reel and a gear pair vibration. The vibration occurs when a handle of the reel rotates. When the vibration is large, an angler feels uncomfortable. In order to measure the gear pair vibration, an evaluation method using a bone conduction speaker was proposed. In this method, the bone conduction speaker is attached onto the handle knob of the reel, and the slight vibration is measured. The measured data was analyzed by spectrogram and FFT (Fast Fourier Transform) analysis, and characteristic data for the forecast of handle rotational feeling in reel were extracted from the result of the FFT analysis. A total of five sample reels were prepared for evaluation. The evaluation points were made into a ranking, and the handle rotational feeling in these sample reels was judged through human judgment. The best estimate for the forecast was defined to be the average of rankings. In the evaluation for the relationship between handle rotational feeling in reel and the measured data, the MT-system of robust engineering was used. In this analysis, a forecast value was calculated based on these characteristic values. As a result, although the vibration was quite small, it was confirmed that there is a strong relationship between the two. Thereby, it becomes possible to make quantitative judgment. During the judgment, an inspector can hear the vibration sound amplified from the speaker, similar to that of the rotational feeling conducted from the handle. Consequently, the judgment becomes easier, and the judgment accuracy improves dramatically.
The webs such as paper, plastic film and thin metal are produced by Roll-to Roll manufacturing system, and are wound into a roll in the final process of this system. However, if the winding conditions of the web are inappropriate, the defects such as gage band, wrinkle and slippage will occur in wound roll, and then quality of products is significantly reduced. In previous studies, some analysis models of in-roll stress considering various factors, have been established to predict the defects. However, as far as authors know, there is few research regarding the gage band. In particular, the plastic films used for high functional flexible devices are being thinner, the defects can occur easily. In this paper, the in-roll stress analysis considering the web thickness variation in width direction and compressive deformation of web in the radial direction using the Hertz contact theory is presented. Moreover, optimization of winding conditions is conducted to prevent simultaneously the gage band, wrinkle and slippage. As a result, it was confirmed that the presented analysis can estimate the radial stress distribution of wound roll in the width direction. And, the effectiveness of optimized wind-up tension is verified theoretically and experimentally.
The characteristics of iron (Fe) and nickel (Ni) diffusion in molten lead-bismuth eutectic (LBE) were investigated experimentally by using capillary method. The diffusion coefficients of iron (Fe) and nickel (Ni) were determined from measured axial concentration distributions of Fe and Ni in LBE specimens. The correlation of the diffusion coefficients can be obtained as DFe =3.5×10-3exp (-4.15×10-4/RT) (550°C < T < 650°C) [cm2/s], DNi =1.7×10-3exp (-3.63×10-4/RT) ( 500°C < T < 650°C) [cm2/s]. The diffusion coefficient of Fe in LBE obtained is approximately the same as the result derived by Balboud - Celerier. The result of the diffusion coefficient of Ni is almost the same order of magnitude as that of Fe, in spite of much higher solubility of Ni than that of Fe in LBE. From microstructure observation by using the scanning electron microscope (SEM) and the energy dispersive X-ray spectroscopy (EDX), it is found that in case of Ni diffusion, some compounds composing 50-60% Ni, 15-20% Pb and 15%-20% Bi, were observed in the solid specimen. It is estimated that the formation of the compounds slowed down the diffusion of Ni into LBE.
The aim of the present study is to demonstrate the quantitative measurement of the spatio-temporal fluctuation of the heat transfer in a water pipe flow around an orifice plate. In the present study, a technique using high-speed infrared thermography was used to measure the heat transfer. The measurement was first performed for a fully developed pipe flow without installing an orifice plate in order to verify the validity of the measurement technique. The spatio-temporal distribution of the heat transfer coefficient was evaluated based on the temperature fluctuation of a heated thin-foil measured using high-speed infrared thermography, and the results indicated that quantitative measurement was possible not only for time-averaged values, but also for fluctuating values. The technique was then used to measure the heat transfer to the flow around an orifice plate (the bore ratio was approximately 0.5). As a result, it was revealed that the heat transfer downstream of the orifice fluctuated violently, and the instantaneous structure of the heat transfer was remarkably finer than the streaky structure for the fully developed pipe flow. The time-averaged value of the heat transfer had a maximum at approximately two diameters downstream of the orifice, where the rms value of the fluctuation and its characteristic frequency also became much higher than those for the fully developed pipe flow.
This study presents a new navigation system consisting of a resource-constrained rover and landers for planetary long-range exploration. During the exploration, they communicate with each other using radio and the rover receives signals from the landers which contain Angle of Arrival (AOA) data. The rover estimates its position using AOA data. Although obtaining AOA data generally requires a complex device and is difficult to apply to navigation for small rovers. In this study, we implement AOA-based navigation for a resource-constrained rover by rotating a directional antenna such as the high-gain antenna of the landers. In this case, since the rover obtains signals containing AOA data intermittently, we employ an event-driven extended Kalman filter to implement real-time navigation. Our proposed method has the advantage that the rover does not need navigation cameras or sun sensors, and it is therefore suitable for resource-constrained rovers. We developed a small rover and several landers, and conducted experiments in a wide range of Black Rock Desert in America, using the small rover and the landers to obtain the experimental data of AOA which is difficult to simulate. The experimental data are used in numerical simulation. We also validate some cases where there is one lander. These results show the effectiveness of our proposed navigation system using AOA data from the landers in long-range exploration.
This paper proposes the novel design of a positioning control system of a piezo-ceramic actuator. Piezo-ceramic actuators have been used extensively in many engineering applications which require high precision positioning. However, it is well known that piezo-ceramic actuators exhibit hysteresis in their response to driving input which considerably deteriorates positioning accuracy if no appropriate compensation has been made. Huge efforts have been devoted to the design of control system for positioning control of a piezo-ceramic actuator and a number of different control strategies are proposed for its hysteresis compensation. This paper tackles the problem of the compensation of rate-dependent hysteresis of a piezo-ceramic actuator. Rate-dependence of a hysteresis means that its behavior will vary if the rate or the frequency of the driving signal of the actuator changes. This paper proposes the use of two radial basis function neural networks (RBFNN) to construct a high precision positioning control system of a piezo-ceramic actuator which exhibits rate-dependent hysteresis. The proposed control system takes the form of the internal model control (IMC) system, where one RBFNN is used as the internal model of a piezo-ceramic actuator having rate-dependent hysteresis while the other RBFNN is configured to work as a controller of the system. It is shown in this paper that RBFNN model trained with particle swarm optimization (PSO) algorithm provides good modeling performance for a wide range of driving frequency, and the RBFNN controller is made adaptive with back propagation on-line parameter updater to cope with possible modeling inaccuracy between the actuator and its model. Results of the positioning control experiments indicate that proposed adaptive internal model control system with two RBFNNs shows adequate performance on the compensation of rate-dependent hysteresis to guarantee high precision positioning.
This paper deals with the wave absorbing control of a suspended simple pendulum system by the lateral motion of the support. The control acceleration of the support was derived by the connecting condition of real pendulums to the wave-controlled multiple simple pendulums virtually existing above the support. The wave propagating solution of the homogeneous multiple simple pendulum system was theoretically derived and applied to the virtual pendulum system. The velocity and position feedback control of the support was added to the support acceleration for wave control because the wave control could not fix the support position. This control can place the support at other than the original position. The experiments of a three homogeneous rigid pendulum system and a rope-and-mass system were conducted. The rope-and-mass experimental system has the function of winding up and down of load mass. The effect of the virtual pendulum length on the wave control was also investigated. From the simulation and experiment, our presented control strategy was shown to be effective enough and practical for real crane systems.
A magnetic bearing supports a rotary shaft without any contact by magnetic force, but such a system is complex due to additional mechanical and electrical components. In order to reduce the size and complexity of the driving circuit of the bearingless motor, this paper proposes a magnetically levitated shaded pole induction motor. The rotor is still supported by magnetic force, but the motor has a very simple structure because magnetic levitation and rotation can be achieved with only one amplifier. The operating principle of the shaded pole motor was confirmed by FEM magnetic field analysis. The suspension force and rotational torque have also been analyzed. It was found that in order to support and rotate a rotor, large amount of current is required. A simple experimental setup using a commercial shaded pole induction motor was designed and fabricated to verify the validity of the FEM analysis. In the test system, the rotor is supported by a linear rail that allows the rotor free rotation and free movement in a vertical direction but not in a horizontal direction. According to the measured step response, stable magnetic levitation suspension was achieved despite a relatively slow settling time due to the large friction force in the horizontal direction.
This paper derives closed-form solutions for the local deformation of a bi-convex boom under circular bending, and the resulting strain energy and self-extending force. Convex tapes and bi-convex booms that consists of a pair of convex tapes can be stored into a small volume and have high specific rigidity. They extert a self-extending force when stored cylindrically. Therefore, they have been proposed as members of deployable space structures. In this paper, two types of bi-convex booms are considered. In the first, the tapes of the bi-convex boom are bonded to each other at their edges; in the second, the tapes are wrapped in a cylindrical braid mesh. The latter is called a BCON (braid-coated bi-convex) boom. The tape of a BCON boom can slip on each other, and do not separate from each other because of the tension of the mesh net. Consequently, the BCON boom can be used in an ultralight self-deployable structure with quite high stowage volume efficiency and specific rigidity. However, structures using convex tapes or BCON booms have been designed and developed through a trial-and-error process because there is no appropriate formula for the self-extending force of convex tapes. This paper proposes a formula for the deformation of a convex tape that is initially bent into a circular shape. The deviation from the circular shape is obtained by solving the equilibrium equations. The deformation of a bi-convex boom is also derived by using the solution for a convex tape. Thus the theory described in this paper contributes to the design of space structures using convex tapes in bi-convex booms, as well as to the structural mechanics of flexible beams.