Fullerene C₆₀ has been attracting attention as a kind of lubricant. In this experiment, four kinds of lubricants oil with different concentrations of fullerene were prepared for the purpose of extending the service life of bicycles, for which demand has been increasing in recent years. These lubricants were added to the contact area between the pin and the roller of the chain, and then durability tests were conducted using a chain testing machine to confirm the effect of fullerene as an additive. The amount of movement of the sprocket on the driven side of the linear guide was measured with a displacement sensor, and the amount of elongation was measured. The results showed that the amount of elongation decreased with the use of fullerene lubricant, and the amount of elongation was the lowest when the fullerene concentration was 2000 ppm. It was also found that there was no significant difference in the amount of elongation between 100 ppm and 1000 ppm.

The objective of this study is to investigate the forces acting on the end surfaces of pins and motions of pins of chain type CVT. The contact force acting on the end surfaces of pins under torque transmitting condition was measured by strain gauges attached on a modified pin of which the thickness was partly reduced by machine work. The time history of strains was measured under torque transmitting condition by data logger equipped on the chain belt. The motions of pins in pulley groove were also investigated by using transparent pulley made from acrylic resin. The digital camera was used to investigate the angle between leading and following pins of chain. Test results showed that the bending deformations of pins were confirmed by contact force applied by pulley surfaces. The position where the contact force acts was also calculated by assuming the pin was simply modeled as a beam that eccentric compressive load was applied. Calculation results showed that the position of contact force was moved by motion of pins in pulley grooves. The observations also revealed that the angle between leading and following pins of chain were rapidly changed at entrance and exit of pulley grooves when the wrapping radius of chain was large.

In order to reduce the loss of the metal belt CVT, research is being conducted on texture patterns that reduce the radial μ of the pulley. In order to verify the effect, pulley with this texture of some patterns were mounted on a metal belt CVT tester, and the power transmission efficiency and inter-axis force were measured. As a result, it was confirmed that the inter-axis force increased compared to the normal pulley without texture, and the possibility of μ decrease in the radial direction of the pulley was confirmed. In addition, the power transmission efficiency was 0.4 points higher than that of the normal pulley.

Since traction drives need high contact force to transmit power, high contact pressures arise at the points of contact between rollers. These pressures cause failure through rolling contact fatigue. Therefore, prediction of the rolling contact fatigue strength is essential during the design of a traction drive. If clean steels with reduced density of inclusions in materials is used, there is a possibility that the improvement of rolling contact fatigue strength and decrease of the scatter of strength. In this study, the rolling contact fatigue strength and scatter of clean steel rollers were evaluated by experiment. As a result of experiment, the rolling contact fatigue strength was 1156.2 MPa and the standard deviation was 15.4 MPa. In case of ordinary steels, the rolling contact fatigue strength was 1008.7MPa and the standard deviation was 85.0 MPa. From this fact, the rolling contact fatigue strength for 10⁷ cycles improved by 14.6% and the standard deviation was decreased by 69.6 MPa when clean steel was used.

Motors for electric vehicles are expected to be equipped with reduction gears for traction drives suitable for high-speed rotation to make them smaller and more efficient. However, if a large amount of lubricating oil is supplied, large agitation resistance due to lubricating oil is generated around the roller, which is thought to cause energy loss. Therefore, we focused on the friction reduction effect by microbubbles in this study. If the microbubbles enter the contact point, there is a risk of breaking the oil film and making direct contact. As a result of visualizing the flow around the contact point, the risk of direct contact was judged low. Therefore, the roller was immersed in lubricating oil mixed with microbubbles to visualize the wall flow of the rotating roller. The visualized results were analyzed using the PIV analysis, and the effect of the microbubbles on the stirring resistance was evaluated from the difference in flow velocity between the roller with and without micro bubbles. The results of the PIV analysis showed that the speed was reduced in the case of lubricating oil mixed with microbubbles.

A re-tightening method is generally used to check whether the bolted joint has been tightened with the prescribed tightening torque. The advantage of the re-tightening method is that it can be easy to check the tightening torque. On the other hand, the tightening torque in re-tightening process becomes always larger than the initial tightening torque because static coefficient of friction at mating thread surfaces and mating bearing surfaces is higher than dynamic coefficient of friction. Consequently, the tightening torque in re-tightening process causes excessive clamping forces on the joints. Therefore, it is not easy to estimate the initial tightening torque accurately without the excessive tightening torque and clamping force. In this study, we have proposed a new re-tightening method to estimate accurately the initial tightening torque without increasing the clamping force. In the re-tightening process, the gradient of the tightening torque T to the rotation angle θ in the re-tightening process. We have conducted the experiments using M8 steel bolts. As a result, the initial tightening torque estimated with an error of less than 10% in all conditions.

Screw loosening tests are often performed with a size of about M10. Ease of load application to screw fasteners and ease of measurement of axial force for detecting loosening are the main reasons. In comparison with that, in the loosening test of small diameter screws, since the sample of the test is small, it is difficult to detect the load applied to the screw fastener, addition of displacement, loosening, and the like. This study proposes a method of looseness test and a method of detecting looseness for a small diameter screw of about M1. In this study, we proposed a method to test for screw loosening using inertia. We also proposed a method to detect the occurrence of looseness during the test. Experiments were performed to confirm that they were effective. Using this method, we evaluated small-diameter screws made of metallic glass, which has the characteristics of high strength and low Young's modulus, and found that they are difficult to loosen.

For mechanical elements such as gears and bearings, it is necessary to know the contact stress state in order to reduce damage and improve life. The geometrical contact of mechanical elements includes surface contact, line contact and point contact. When the rolling bearing sliding surface has three-dimensional contact, it is necessary to analyze the three-dimensional contact stress. However, it is difficult to calculate the three-dimensional Hertzian pressure because an analytical solution cannot be obtained. Therefore, we report an example of calculation of the Hertzian auxiliary function required to obtain the three-dimensional contact pressure.

Because of increasing number of motors which used for cars and spread of hybrid vehicles and electric vehicles, rack & pinion gear which used for automotive electric power steering is required to improve transmission efficiency. In former research, it was found that sliding velocity is related to transmission efficiency. In this research, new test rack & pinion gears which designed by focusing sliding velocity are designed and made. And their transmission efficiencies are measured. As a result, it found that the smaller sliding velocity is, the higher transmission efficiency is. And, the larger sliding velocity is, the lower transmission efficiency is. Result of this research suggested the method designing high efficiency rack & pinion by focusing gear dimensions related to sliding velocity and making module smaller, tooth depth smaller, number of teeth larger, and rack shift coefficient smaller in order to make sliding velocity smaller.

The purpose of this paper is measurement of friction loss by meshing of Spur Gears and evaluation of the influence of base oils. Three types of lubricant oil which is Mineral-Oil-Based Automatic Transmission Fluid (Gr.Iand Gr.III) and Polyalphaolefin -Based Automatic Transmission Fluid (Gr.IV) were used. The measurement was carried out in case of three different oil temperatures, and three different circumferential speeds. Frictional loss is measured by using the back-to-back gear tester. In order to separate the friction loss, windage loss, churning loss, seal loss and bearing loss were individually measured. As a result of these measurements, two tendencies were shown. Firstly, as the oil temperature increases, friction loss is decreased. Secondly, friction loss also decreased with increasing circumferential speed. Lowly Viscosity and lowly Pressure viscosity coefficient is effective for the power transmission efficiency of the gear.

In the previous study, the rolling contact fatigue life of case-hardened steel was improved by the cavitating jet in water with an injection pressure of 20 MPa. In this study, the cavitation peening apparatus with a maximum injection pressure of 35 MPa was designed and manufactured, and the optimum cavitation peening condition was determined quantitatively. From the result of the erosion tests, the peening intensity of the cavitating jet in water with an injection pressure of 35 MPa was larger than that of 20 MPa. In addition, the compressive residual stress of stainless steel became the largest by the cavitation peening using the nozzle geometry induced the maximum mass loss in the erosion tests. In the rolling contact fatigue tests, the rolling contact fatigue life of case-hardened steel was improved by the cavitating jet in water with an injection pressure of 35 MPa. However, the cavitating jet in water with an injection pressure of 35 MPa was inferior to that of 20 MPa in the rolling contact fatigue life of case-hardened steel. The reasons for this include that the surface roughness of case-hardened steel was increased by the cavitation peening with too long processing time.

Since gears transmit motion by meshing teeth, it is hard to avoid problems which wear and damage to the tooth surface. Because Tooth surface wear is difficult to predict, the approach to the wear problem still often relies on empirical rules and symptomatic measures. If the undermining by wear can be predicted by mathematical formulas, it may allow engineers to solve wear issues in model-based development, or to consider wear resistance from the design state. Therefore, the development of wear prediction formulas seemed like a very valuable goal, so the authors decided to work on it. In this paper, as the first step for the final goal, the gear driving test was conducted using multiple gears with different tooth surface roughness. Then relationship between tooth surface roughness and wear, or other surface damages, was investigated.

There is a need to have a highly accurate method of estimating meshing friction loss in order to improve the efficiency required of automotive transmissions. The friction coefficient for calculating meshing friction loss can be estimated accurately with the formula proposed by Matsumoto and coworkers, which uses the ratio of the sum of the maximum surface roughness of two tooth surfaces, Rz, to the minimum oil film thickness. However, for some smoothly finished gears, estimation accuracy may decline due to differences from conventional tooth surface properties. In this study, experiments were conducted to measure the meshing efficiency of gear pairs with different tooth surface roughness and properties. It is shown that the friction coefficient was estimated with greater accuracy by using the lambda ratio value that is employed as a parameter of the oil film thickness on bearings.

There are various factors in hobbing processes that affect the profile deviation and helix deviation of gears. Accordingly, it is difficult to analyze the problems on the hobbing machine from the profile and helix deviations of the hobbed gears. Therefore, we have developed a system with artificial intelligence that estimates the motion errors in a hobbing machine from the profile and helix deviation of the hobbed gears. First, hobbing simulations provided the data on profile and helix deviations of hobbed gears, and correlation coefficients expressed the similarities of the simulated micro-geometries between tooth flanks. The correlation coefficients constituted the images used for training artificial intelligence. In the present paper, we compared the images created from the hobbing simulations with those obtained by actual hobbing processes and examined the possibility of the images constructed with the hobbing simulations in training artificial intelligence. As a result, the images showed the decent possibility of the training.

Despite the declining birthrate and aging population, the labor shortage in the long-term care industry has not been improved due to the heavy burden on long-term care workers. Against this background, various transfer assistance robots have been proposed. We are currently investigating a robot that can assist in transferring a patient from a nursing bed to a wheelchair. The transfer assistance robot needs to be created taking into account the various body size differences of the caregivers. This paper describes the dimensions and mechanism of the nursing robot according to the difference in body size. Also, we design a nursing care robot that can be transferred comfortably by reducing the physical and mental burden on the person being assisted.

With the growing population of elderlies, the number of senior citizens coping with walking impairments is increasing. It is necessary for elderlies to do proper exercise to prevent systematic disease. Various type of walking assistant devices is invented for rehabilitation or exercise support. However, doing exercise needs high level of motivation to gain effective result. Maintaining a high level of motivation is a critical issue during exercises since it might involve pain, discomfort, or depression especially for elderlies. On the other hand, senior citizens have higher possibility get injury caused by over-exercising. Therefore, the purpose of this research is keeping positive emotion and body condition for senior citizens when they doing exercise using walking assistant device. In this research, we proposed a 3D human condition model to evaluate human emotion and fatigue condition. For emotion recognition, we proposed a Deep Neural Network (DNN) trained by electroencephalogram (EEG) signal and heartbeat signal. For fatigue detection, we proposed a new method by using portable near-infrared spectroscopy (NIRS). In addition, we also found the relationship in living habit and fatigue time. Based on the emotion evaluation system, we can propose a control strategy. By using the control strategy, user can keep doing exercise in high level of motivation while avoiding fatigue damage.

It is important for rehabilitation assist suits to ensure the safety for patients even when their computer fails and becomes uncontrollable. We have developed a compact and light velocity-based mechanical safety device (Compact VBMSD) for an elbow joint assist suit. The Compact VBMSD stops the assist suit’s motor when it detects an unexpected elbow joint angular velocity. The Compact VBMSD works even when the assist suit’s computer breaks down, because it consists of only passive mechanical elements such as springs. However, it is difficult to attach the Compact VBMSD to various assist suits because the Compact VBMSD was designed to incorporate into the elbow joint assist suit. In this study, we propose an external velocity-based mechanical safety device to be attached to various assist suits. First, we describe the overview and the structure of the external velocity-based mechanical safety device. Second, we explain the mechanism of the external velocity-based mechanical safety device. Finally, we present the external velocity-based mechanical safety device which we designed.

We developed a new stair walking assistive device for the elderly. By utilizing the phenomenon of the stretch reflex of the bi-articular muscle, user can raise his/her foot higher than the normal by only assisting the ankle joint. Then the can climb up stairs easily. On the other hand, to prevent bending the knee joint while climbing down, the wedge effect mechanism which was used multi-thread worm and helical gear was developed. The experimental results can be shown the effectiveness of them.

Last years, the interest in walking increases, on the other side people that keep feeling anxious for it are considerable. But when cripple or elderly people use simple walking assist tools like a stick and a hand craft, they will walk with an inadequate posture as a slouch, and it may be in dander to lead accidents with that as a cause. In this study, the walking assistance device with hind legs that support trunk from backwards was proposed. The driving system of these hind assistant legs that perform like sticks following user’s walking by cams are shown. The experiment was done with motion sensors put on it. In this experiment, motions of the linkage in the unloaded states of hung up with a rope were measured, to confirm the motion produced only the device. And assessed statics efficiency on it was done. Statics relations between the link that drove by user’s gate and the other one that contacted ground as an assistance leg were experimented and timing that need auxiliary torque was confirmed.

The water jet impact acoustic method is the wall inspection method to detect the concrete flaking by analyzing the sound generated by the water hit on the structure. The authors are developing the completely constrained planar CDPR (cable-driven parallel robot) to move and position the device for this method facing the wall. In general, the planar CDPR has relatively low rotational stiffness about the axes on the motion plane, which gives a non-negligible effect on the positioning accuracy of the water jet. Therefore, in this paper, the fin-like chains which mechanically improve the rotational stiffness about the axes on the motion plane are proposed. They are rigid-body chains, which can rotate only around the normal axis of the motion plane. The effect of the mechanism is discussed through the analysis using the stiffness matrix and the stiffness measurement experiments using the prototype.

Robots are being used in well-designed environments such as in factories. Walking is superior to wheeled locomotion in that it can pass over steps and discontinuous surfaces, and bipedal robots are expected to be consistent with environments designed for humans. To improve stability in bipedal robots, use of control moment gyro (CMG) has been proposed. A CMG is a mechanism that rotates a lightweight flywheel at high speed and extracts large inertial force through the gyroscopic effect. The extracted inertia force is used to control the robot's posture, and stable walking is achieved. The simplicity of the robot can be improved if the torque of the CMG is utilized not only for posture stabilization but also for motion generation in an integrated manner. In this study, as an example of a robot that uses CMG torque not only for posture stabilization but also for motion generation, a quasi-passive walking mechanism that moves only by the output of a single CMG unit is proposed. Using the quasi-passive walking mechanism driven by self-excited oscillation as a reference, a method is devised, in which the CMG causes oscillation in the roll direction and the legs swing out by gravity. A walking mechanism with legs of 270 mm in length was fabricated, and the successful walking of the proposed mechanism was confirmed.

This paper proposes a novel method for manufacturing a minute-sized metal nut having a twisted groove with a square cross-section. The manufactured nut engages with our proposing ultra-small diameter and long lead Gaudi screw as a component of the miniature differential screw mechanism. A notable idea is first to machine a spiral shape that splits the nut along with the corners of the square cross-section screw then cut and combine them. Using the proposed manufacturing method, we have realized the production of left and right twisted nuts with a square cross-section, a side length of 2 mm, a lead of 10 mm, and a total length of 4 mm. The divided nut parts were incorporated into a holder created by the stereolithography method and fixed using a cap designed with a particular shape. The manufactured nuts are combined with the miniature Gaudi screw then verified functions as a differential screw mechanism.

Aiming to generate various motions of an underactuated marionette robot, the novel design method with less actuators is proposed and is experimentally examined. The marionette robot is composed of a human type puppet with 12 DOF and with only passive revolute pairs and a controller with six sliders moving on six rotating arms which drive the puppet with wires. The forward kinetostatics analysis can be achieved with the optimization to minimize gravitational potential energy of the puppet. The minimum necessary actuators configuration for the desired motion of the puppet can also be obtained with the inverse kinetostatics analysis to minimize motion error. Since a prototype can experimentally generate the desired various motions while changing sliders to be fixed, it is confirmed that the proposed method is effective and useful.

Rolling bearings are machine elements that are often used in rotating machinery, and their faults can cause serious damage of the rotating machinery. In particular, a sudden fault such as flaking gives a significant impact to rotating machinery, so early detection of fault is very important. There has been many researches on damage diagnosis. However, in many cases, simulated damaged bearings are used because it is difficult to obtain actually damaged bearings. It is necessary to develop a device that can cause rolling fatigue damage to bearings more naturally in a short period of time. The purpose of this study is to develop a equipment that can generate flaking and to clarify technically important points for designing such equipment. The equipment is designed using basic rated life. The amount of decrease of interferences in the fittings between the bearing and axis/housing are taking into account. The jerk sensor and the damage diagnosis method developed in our laboratory were used for the tests. The test results showed that three event of flaking were successfully generated in two bearings.

Rolling bearings are fixed at the both ends of a shaft. In order to avoid the effect of expansion of shaft by heat generation, clearance fit is designed between the outer ring and the housing. Thus, one end of the shaft can move to its axial direction. Though a recommended clearance according to the amount of load is listed in a trade catalogue, a free-end bearing may wreck due to axial unmoving of the shaft on ground of fixing inclination between the shaft and the free-end bearing. In this study, axial movement of free-end bearing caused by axial movement of shaft was observed with a simplified equipment. Consequently, the axial displacement, the load required for axial displacement, etc., was clarified.

Meniscus and cavitation are formed around the EHL contact area of rolling elements in many machinery. Their shape affects to the lubrication state of the EHL contact area. Especially if the rear part of the meniscus breaks, the amount of lubricating oil supplied to the next EHL contact area decreases, and it is caused oil starvation. The shape of the meniscus changes depending on the oil supply conditions. However, there are no cases in previous studies that focus on the relationship between the oil supply conditions and the shape of meniscus. Therefore, in this study, we observed change in the meniscus and the cavitation due to changes in oil supply conditions under higher peripheral velocity condition than previous studies. We also calculated the pressure distribution inside the meniscus by pressure estimation utilize PIV analysis result. As a result, it was confirmed that the cavitation does not change above a certain peripheral speed. It was also confirmed that the decrease in pressure inside the meniscus was suppressed as the amount of oil supply increased.

Gas foil bearings are one of air bearings with a flexible bearing surface that can support the shaft in a stable condition. As a result, they have a higher damping performance than other air bearings. Since bearing characteristics is deeply dependent on the support structure, various support structures have been proposed. However, due to the complexity of the support structure, analytical evaluation is difficult. Therefore, empirical design is often used and the development speed is slow. In this study, a design method for foil bearings is proposed utilizing topological optimization which does not rely on the designer's experience. Characteristic analysis of the foil bearing with optimized support structure shows that increasing the flexibility of the leading edge results in a uniform film thickness at the trailing edge and increases the load capacity. Furthermore, by fixing the support structure at the rear, it was found that the load capacity could be maintained even when a large fluid force was applied.

The oil film behavior in a journal bearing was observed utilizing a photochromism visualization technique that uses an oil film that changes color when irradiated with ultraviolet light as a tracer. This method is an innovative technique that enables simultaneous measurement of oil film flow and oil film thickness. In the end-expanded gap of a journal bearing, a gas-phase region is generated due to negative pressure and the drawing in of air. Since cavitation greatly affects bearing performance depending on its condition, it is important to understand it by direct observation of the bearing surface. In this study, a sapphire journal bearing with a transparent surface was used for observation. By coloring the inside of the gas phase, it was possible to simultaneously observe the oil film that stays on the bearing surface and the oil film that moves with the shaft. From the difference in the thickness of the oil film on the bearing surface and the shaft side, the location of the gas phase can be determined.

Floating bush journal bearings are widely used to support small-sized high-speed rotating machinery. When the shaft rotational speed exceeds a stability threshold speed, the bearing shows self-excited vibration. However, the vibration could be disappeared when the speed further increases and the bush rotational speed levels off. The phenomenon can be explained qualitatively by applying the hydrodynamic lubrication model with the axial oil film rupture being considered. However, the predictions are in quantitatively poor agreement with the measurements. Therefore, one of the authors aims to improve the model based on the phenomenon observed experimentally by using a test apparatus of a cylindrical bearing that corresponds to a high-speed floating bush journal bearing. In this report, the bush driving torque due to oil film viscous force is measured with the experimental apparatus that the oil feeding system is a little modified and is related to the oil film width reduction phenomenon observed in the previous report. The results imply that they are related to each other. The effect of oil supply pressure is also investigated on the bush driving torque. It is found that the torque measured under the lowest oil supply pressure is in qualitative agreement with the numerical predictions.

The purpose of this study is to estimate force characteristic of short-length McKibben type artificial rubber muscle using artificial muscle model. In previous works, we proposed mathematical model of McKibben type artificial rubber muscle considered the hysteresis characteristics and estimated the force characteristic of long-length McKibben type artificial rubber muscle based on proposed model. However, the force characteristics of short-length McKibben type artificial rubber muscle can not be estimated because it can not be represented as the virtual pantograph in the previous model. Thus, the virtual pantograph structure is augmented based on the ratio of diameter to length for applying to artificial muscles of various lengths. In this paper, the augmented model was compared with the force characteristics of actual McKibben type artificial rubber muscles of various lengths. From the results, it was confirmed that proposed model can estimate the force characteristics of short-length McKibben type artificial rubber muscle.

In this study, we are developing a flat-string type integrated artificial muscle (FIAM) that consists of thin McKibben-type artificial muscles by a flat-string string-making machine. The FIAM has features such as flexibility, lightweight, thinness, and high contraction ratio. In this report, we examined the combination of an optical fiber sensor for the displacement estimation of the FIAM. The optical fiber was integrated into the FIAM as a sensor, and it was confirmed that the sensor output changes with the contraction of the FIAM.

Actuators that drive in extreme environment such as high or low temperature environment and radiation environment has been researched. The actuators are expected to be contribute to various fields such as space exploration, deep sea exploration and rescue robots. In this laboratory, a soft actuator composed only of polyimide (PI) films and driven in an extreme environment has been developed. In this study, a method of welding for PI films by using a unit that integrates functions of a mold and a heater was proposed. The unit is fabricated by using printed electronics technology. This welding method does not require pretreatment of films, adhesives or additives. In addition, welding of various shapes is possible in a short time. To examine whether pneumatic actuators can be fabricated by this method, welding strength and maximum pressure resistance of air chamber were evaluated. The average welding strength was 521 N/m. In the pressure resistance test, the air chamber was damaged when the applied pressure was 98 kPa. As a result, it was confirmed that the air chamber welded by this method had sufficient pressure resistance to manufacture pneumatic soft actuators.

An asymmetric variable lap spool valve for hydraulic control system is proposed. The spool of the control valve with asymmetric notches on its land is operated by a linear/rotational two-degree-of-freedom actuator. The flow characteristics near the neutral position of the spool can be continuously changed according to the operating condition of the hydraulic actuator, the flow characteristics of the over- and under-lap valve can be continuously switched, and the flow characteristics of the meter-in and meter-out circuit can be switched as well. This paper reports that an asymmetric variable lap spool valve operated by a linear/rotational two-degree-of-freedom actuator can suppress cavitation during the control of a hydraulic actuator with inertia load

In this research, a prototype model of six degrees of freedom (6-DOF) parallel mechanism stage for fixed head type of 3D-printers was designed and fabricated as a new additive printing method for a surface of three-dimensional objects. Operating performance and the results of additive printing on the three-dimensional object ware investigated. In this actuator system, the head for additive printing is fixed to the upper part of the movable stage and the three-dimensional object is placed on the stage. It can move with 6-DOF by a slant direct drive type of parallel mechanism. The results of additive printing depend on the positioning accuracy of the movable stage. In this report, the verification of the positioning accuracy of the movable stage is experimentally investigated.

In this study, since we aimed to develop a device to evaluate dexterity by using illusions, we firstly developed and tested a device to generate cutaneous rabbit illusions. Then, we conducted a series of psychological experiments to investigate the relationship between the cutaneous rabbit illusion and the stimulus position, and one and the stimulus time difference. The results of the performance test showed that the system had sufficient time difference resolution. Furthermore, it was found that the distance between 75 mm and 125 mm, which was the distance between the second and third stimuli, was sufficient to produce the illusion, and that the longer the time difference between the second and third stimuli, the harder it was to produce the illusion.

Lack of muscle strength due to aging causes reduction of stable gait motion. Rehabilitation for the recovery of trunk motion during walking and muscle strength are important to obtain stability of walking. In this study, we developed wearable device which can correct a posture and assist trunk rotation to support exercise therapy for people declined in ability of walking. Proposed device is composed of some resin parts with built-in ball bearing structure and pneumatic soft actuator such as McKibben type artificial muscle and bellows. The mechanism of proposed device imitates spine structure to realize adjustable stiffness characteristics. In this paper, the mechanism for rotation assist and drive principle of device are described. The extension characteristic of pneumatic bellows is confirmed to estimate assisting torque. Finally, the validity of proposed mechanism was confirmed from experiment result.

This paper presents the design and operating characteristics of an elevator unit, which is a basic element of the proposed air lifter with a high stroke by using a pneumatic soft actuator. By adopting a pantograph type link mechanism for the elevator unit, it was verified whether the table could stably expand and contract. As a result of the experiment, we confirmed that the elevator unit moved at the fixed speed in the expansion and contraction operation, and the table angle in the operation was measured at maximum about 4 degrees in the unloaded condition.

We propose a pneumatic expansion mechanism using three duct hoses for moving in narrow spaces. The duct hoses have high elasticity and flexibility, and by using these two properties, the robot is expected to be used in narrow spaces that are difficult for people to enter. This paper presents the structure and driving principle of the telescopic mechanism, and report on the results of the operation tests.

For maintenance of pipes in industrial plants and so on, in-pipe microrobots that perform power-needed tasks have been required. We have called this kind of robots the power microrobots and developed them using high density hydraulic power. We have proposed and developed a micropump using fluid inertia as a micro hydraulic power source. The micropump called the FI micropump is a piezoelectric reciprocating pump that has an outlet pipe in place of an outlet check valve and generates high hydraulic power using the fluid inertia effect in the outlet pipe. In this study, a 10 mm diameter in-pipe mobile microrobot using a short length FI micropump was proposed, designed and characterized. The robot has shorter length without space dedicated to retain the working fluid by using the hydraulic microactuators as tanks. The detailed robot structure was proposed. Then, on the basis of the simulated characteristics of the short length FI micropump, the traveling characteristics were theoretically clarified.

The incorporation of the limitation of the tangential contact stress with the increase of the normal contact stress is required for the analysis of the friction phenomenon of solids subjected to the high normal contact stress, which cannot be described by the Coulomb friction condition. The subloading-friction model is extended to describe this fact in this article.

In this study, a new analytical model is developed to evaluate the frictional properties of plateau surface structures by numerical simulation. Specifically, the plateau surface structure is modeled using a Bi-Gaussian roughness model, and the model is implemented in a FEM analysis to demonstrate, for example, that the effect of changes in plateau fraction on the Stribeck curve can be easily quantified. The model can be applied to a wide range of applications, such as the evaluation of the effect of anisotropic roughness at the valleys of a plateau surface structure on frictional properties, and frictional simulations that take into account shape and roughness changes due to running-in processes. Therefore, it is expected that the model is expected to be a useful tool for CAE of sliding surface design.

In recent years, detailed analyses of lubricating oil flow using computational fluid dynamics were carried out for fluid lubrication on textured surfaces. Most of them are performed for steady state and with use of a fixed geometry. However, the unevenness on the surfaces moves each other in the sliding region and the film thickness and the geometry change. Therefore, it is necessary to perform unsteady analysis with use of the geometry changes. The purpose of this study was to obtain knowledge about the of sliding characteristics on the textured surface considering the unsteady state. Immersed boundary method is used for reproducing for the geometry changes on the texture. From the analysis results, it was clarified that the shape of the sliding surface has a large effect on the sliding characteristics.

The effect of micro-dimples and its mechanism in mixed lubrication region under surface contact condition were researched. First, friction tests were conducted using a ring-on-disk tester and the effect of dimples with various depths on the improvement of sliding properties was evaluated. Secondly, in order to elucidate its mechanism, fluorescence method was used to visualize oil film behavior around dimples. Then, the process of supplying lubricant by dimples to oil film was observed. Thirdly, by observing the flow behavior of fluorescent particles around dimples, the process of trapping wear particles by dimples was also investigated.

Belt-type continuously variable transmission (CVT) is a type of transmission for automobile to enable high-efficiency driving. CVT transmits torque by frictional force, hence high friction is required in circumferential direction of the pully. However, to reduce friction loss, low friction is required in the radial direction of the pully. Therefore, it is important to generate friction anisotropy that satisfies both the frictional characteristics. Surface texturing is one of the effective ways to generate friction anisotropy. In this study, 4 types of groove texture were applied to actual CVT pulley, and their frictional properties were examined. In this presentation, we will report the results of the friction test and explain the effect of surface texture patterns on the generation of friction anisotropy.

A new technology for tuning friction coefficient between rubber and rough surfaces is developed based on friction-induced vibrations occurring in the contact interface. Specifically, we demonstrated that the use of soft rubber film containing hard particles is effective to increase the friction force. In addition, to discuss the mechanism of this friction increasing effect, ‘Tomlinson model’, which describes the energy dissipation due to the jumping of a point subjected to a periodic potential, was introduced. In this study, based on the numerical results of Tomlinson model simulation and some experiments, we discussed the effect of two parameters, i.e., Young’s modules of the soft rubber film and vertical load, on the friction coefficient.

The tribological phenomena that occur between abrasive grains and a work material are extremely complicated, and it is difficult to identify them. In this study, we focused on the change in abrasive machining performance under lubricated condition and investigated the possibility of in-process evaluation. Two AE sensors were attached to each test piece, and dual AE sensing of AE signals generated from each material was attempted. As a result of this experiment, it was found that the AE mean values of both test pieces decreased in the lubricated state compared to the unlubricated state. In addition, from the frequency analysis of the AE signal waveforms, it was found that the AE frequency component (about 0.1 MHz) due to friction increases.

In recent years, an increase of energy efficiency of machines became worldwide request. Therefore, the reduction of friction loss in the sliding part has become an urgent issue. Generally, under high pressure conditions, the oil thickness decreases, resulting in a boundary lubrication condition where direct contact between two sliding surfaces occurs, and the friction coefficient increases. In order to reduce friction in this boundary lubrication condition, diamond-like carbon (DLC) coatings, which are carbon-based hard coatings, has many applications parts. The present paper demonstrates a fundamental study of a new method using electronic field at contact surfaces. We conducted the friction test using a pin-on-disk friction tester. The friction tester had a SUJ2 ball or ta-CNx-coated ball and a soda-lime glass plate. We used 30-μL propylene glycol (PG) as lubricant, and applied DC voltage to contact area during the friction tests. As a result, the friction test with the ta-CNx-coated ball showed a low friction coefficient but no lower friction by electronic field. On the other hand, the electric bias reduced the friction coefficient with the SUJ2 ball.

Diamond-like carbon (DLC) coatings have many applications due to its low friction, high wear resistance, and chemical stability. Especially, the low friction characteristic is obtained due to softness and low shear strength features of the transformed and transfer layers. On the other hand, when the transfer layer is removed due to disturbance, an increase in friction and instability of tribosystem can be occurred. Therefore, in situ treatment methods for DLC coatings, which promote running-in, transformation, and transfer of the carbonaceous structure, are strongly reasonable to realize stable system. In the present paper, we develop a new in situ surface treatment method using surface discharge to DLC coatings. As a result, a friction coefficient reduced from 0.18 to 0.06 with the surface discharge, while no discharge condition showed no running-in behavior. The thicker transfer layers, the lower the friction coefficient. Therefore, the low friction due to surface discharge was considered be provided by the mechanism of the thin solid lubrication theory developed by Halling. Here, we calculated estimated friction coefficients, and the estimated values showed good agreement with the experimental result. In conclusion, the surface discharge promotes development of a transfer layer, and then the soft and thick transfer layer reduces friction of the DLC coating.

By applying a DLC film to the metal surface where the resin solidifies, the peeling strength of the solidified resin-metal interface is reduced. As part of investigating the reasons, we investigated the effect of the Si content in the Si-DLC film on the peeling strength at the interface between the film and PMMA and the amount of polar group on the resin-side peeled surface. As a result, it was found that the higher the Si content in the Si-DLC film, the lower the peeling strength. In addition, it was found from the IR absorption spectrum near the PMMA-side peeled surface that the C=O / C-C peak intensity ratio decreases with the increased Si content in the Si-DLC film.

To implement the cutting and surface modification in one machining process, we proposed a surface modification technique with a compact short pulse laser, which could be easily mounted onto the machining tool. With the local active space produced by the laser and the cutting oil as the carbon source, a hard metal-carbide formed on the metal workpiece is expected. Herein, the laser irradiation experiment was conducted with a pico-second laser on a titanium alloy disk in PAO. Results showed that the hardness of irradiated area significantly increased, and the formation of titanium carbide was confirmed with XRD. In the reciprocating friction test, the irradiation part showed improved wear resistance and lower friction with the increase of effective irradiated laser pulses.