Atuyoshi Miura

Behavior of Traction Oils under Impact Loads

The squeeze film forming ability of traction fluids is studied under impact load by a falling bearing steel ball against a stationary cylindrical surface or flat anvil made of mild steel, bearing steel, or aluminum. The effect of the pressure-viscosity coefficient and of the viscosity is investigated for plastic and elastic impact. For soft materials, oils with high pressure-viscosity coefficients maintain much greater surface separation under impact load. The time fraction of separation by the oil film increases linearly with the product of the pressure-viscosity coefficient and the yield pressure of the anvil material. It decreases with an increase in surface roughness. Similar results are observed under impact on stationary or rotating surfaces. These results can be used to estimate the solidification behavior of traction oils. In the case of the elastic impact for hard materials, the coefficient of restitution of the ball is influenced mainly by the squeeze film effect, which is governed by viscosity ...

Development of Sit-to-Stand Support System Using Ground Reaction Force

This paper shows our developing sit-to-stand support system using ground reaction force to operate device. Computer system control sit-to-support mechanism automatically by information of the user ground reaction force (GRF). The user of this device don’t need to operate the switch or button. This paper shows first prototype device and describe about device control rule, ex-periment results and the found problems of control, at first. Secondly, to solve these problems, experiment device for second prototype design is shown, and experiment method is described. Finally, preliminary results are shown in these experiments.

A Study of Coefficient of Friction of UHMWPE in Various Contact Conditions and Measurement of Contact Temperature.

Wear debris of ultra high molecular weight polyethylene abbreviated as UHMWPE were clarified to be a major cause of osteolysis. So the wear rate evaluation of UHMWPE has to be performed in the research of artificial joint using UHMWPE. But wear evaluation of UHMWPE requires scrupulous procedure. As the wear rate of UHMWPE is strongly correlated to the coefficient of friction, this study was designed to assess a change of the coefficient of friction for various contact conditions. It was found that the contact condition strongly affected the coefficient of friction. Furthermore contact temperature was measured by means of the infrared radiometric microscope and was compared to the lubricant temperature. Temperature rise up to about 12°C was observed in 30 minutes under a condition of the mean contact pressure p = 12.7 MPa and sliding speed 50 mm/s. There was a linear relation between contact temperature and lubricant temperature.

A Study of Bonding Miss on Ultrasonic Wire Bonding.

The ultrasonic wire bonding is widely used in making many kinds of semiconductor devices. With growing demand of down sizing, semiconductor chips become smaller and sraller, which brings about an increment of bonding miss problem which is likely to occur on the sides parallel to the vibrating direction of the ultrasonic wave. As far as a fixing method is concerned for a chip during bonding, the vacuum suction force is generally employed. In order to find a way to settle the problem this investigation was carried out particularly focusing on the strength of the fixing force of a vacuum suction method and vibrating condition of a silicon chip. Some equations were derived to calculate the suction force and a friction moment under an assumed pressure distribution. Furthermore the rate of velocity components between rotation and translation was calculated. A close agreement was confirmed between the experiments and the theoretical results.

A Study of Fixing Force for a Work Utilized Vacuume in Ultrasonic Wire Bonders

In an assembling process of semiconductor devices, many kinds of ultrasonic wire bonders are generally used. In these machines, works are usually placed on a plate with small vacuum suction hole(s) to hold the works against ultrasonic bonding vibration. In terms of bonding condition, bonding points are required to be fixed firm enough to avoid miss bonding. This study was carried out to estimate the holding force of the vacuum suction methods. Some equations were derived to calculate the suction force and the friction moment of a work placed on a plate with a circular or rectangular vacuum hole under and assumed linear pressure distribution. Furthermore basing upon the Reynolds equation, some negative pressure distributions and the holding force of a work were calculated by the FEM. These results were compared, and an approximate correction function was found for the expressions derived. These results were proved to be valid from experiments.

An Investigation of Error in Hall Element Method for Ball Motion in a Ball Bearing.

It is well known that balls in a ball bearing are rotating three dimensionally. But it is not so easy to obtain this three dimensional ball motion experimentally. The only one method ever reported heretofore is the Hall element method developed by Kawakita et al., where some Hall elements are arranged around a magnetized ball so as to detect an orientation of a magnetic axis of the ball. Nevertheless the reported angular velocity has large fluctuation. This study was carried out to find out the cause of this fluctuation to increase the accuracy of the Hall element method. It starts from the derivation of some equations required to calculate the magnetic field around a uniformly magnetized ball. By means of these equations some possible factors are evaluated to cause fluctuation such as miss-alignment of the Hall elements, calculation method for angular velocity components and a slight deviation from the theoretical sinusoidal wave of the Hall voltage. The result shows all these factors have some responsible for fluctuation in angular velocity components especially the deviation from the theoretical curve has a large responsible for it.