Tomio Matsubara

An Infinite-stiffness Aerostatic Bearing with an Exhaust-control Restrictor

The aerostatic bearing is a crucial element for ultra-precision machine tools, and its stiffness should be as high as possible. To obtain an infinite bearing stiffness, we propose a new type of active restrictor. Differing from conventional inflow passive and active restrictors [1], the proposed restrictor controls the air volume exhausted from the bearing surface. Therefore, we have called this active restrictor an exhaust-control restrictor (ECR). Main advantage of the ECR is its stability for the occurrence of pneumatic hammer.

An ultraprecision positioning system using a twist-roller friction drive

Abstract For ultraprecision positioning, the use of the twist-roller friction drive is proposed. To improve the positioning accuracy of conventional twist-roller friction drives, the proposed design has two features: (1) the twist angle between the driving shaft and the driven rollers is very small, and (2) the driven rollers are supported by hydrostatic bearings. The twist-roller friction drive is mechanically a kind of lead screw, and the small twist angle makes the lead of the friction drive less than 0.1 mm. The use of hydrostatic bearing is effective for improving the rotational accuracy of the driven rollers and for eliminating the influence of the fluctuation in roller rotation on positioning accuracy. It has been shown by experiments that the resolution of positioning can be less than 10 nm, and the twist-roller friction drive is suitable for an ultraprecision positioning system.

Starvation in Ball Bearing Lubricated by Oil and Air Lubrication System

An oil and air lubrication system for ball bearings supporting a high speed spindle maintains friction losses and temperature rises in low level comparing with other lubrication systems, e.g., oil jet or oil mist lubrication. In this study, rotating speeds of the ball in an angular contact ball bearing lubricated by the oil and air lubrication system are observed in various oil supply rates. In addition, quasi-static model analysis of the ball motion is carried out. Experiments indicate that the angular velocity of the ball varies with the oil supply rate even at the constant spindle speed. Furthermore, the model analysis suggests that the ball angular velocity is considerably concerned with an inlet film thickness. From the both results, a relationship between a starvation factor in the ball-race contacts and the oil supply rate is derived for the ball bearing under the oil and air lubrication.

Micro Fabrication Using EDM Deposition

This paper describes a metal deposition process using micro electrical discharge machining (micro EDM) to fabricate microstructures. Steel is used for the tool electrode, and the EDM process is carried out in air. By feeding the tool electrode in the vertical direction, a micro rod with 0.14mm in diameter and 2.2mm in height is formed on the workpiece surface. A fillet-like line with uniform thickness is also drawn over the workpiece surface when the horizontal feed is applied independently of the servomechanism of the EDM machine and the horizontal feed rate is kept constant. It is considered from the observation of the discharging surface that the local gap distance at a discharge location becomes larger than that at other locations on the discharging surface and, therefore, the discharge points are not concentrated at a single point but distributed over the discharging surface.

Estimation of pressure viscosity coefficient by high speed and high pressure traction drive test

Traction tests under high speed condition are carried out for a traction fluid and the pressure viscosity coefficient of the traction fluid pressurized in an extreme short duration is estimated by comparing calculated results with the experimental results. Traction tests are performed on two roller traction drive apparatus in the surface velocity range from 18.9 to 44.0 m/s. The experimental results suggest a practical use of traction drive device with the traction fluid used in this experiment. A relationship between the maximum traction coefficient which is important value for the practical design of the traction drive and the Theological properties including the pressure viscosity coefficient is numerically introduced. The effect of the surface velocity on the rheological properties is discussed with comparisons between the calculated results and the experimental results. Consequently, no effect of the short duration on the pressure viscosity coefficient of the traction fluid is found in this experimental condition.

Oil Film on Water Fog Metalworking Fluid

Many types of ecological-friendly machining technologies have been developed in the last ten years. In this paper, a new type of metalworking fluid is introduced, where comparatively large water particles (fog) are covered with vegetable oil film and sprayed on a machining point with a soft air jet. Better machinability is obtained in the milling test for the oil film on water fog, compared with the conventional emulsion coolant. Machining performance is studied by changing the oil type and the supply condition.

Shear Behavior of EHL Film on Practical Traction Test

In this report, many traction tests are carried on in order to investigate shear behavior of EHL film on traction fluid under practical conditions. The conditions in which the experiments performed are selected considering those of practical traction devices, e.g. automotive CVT, etc. From the traction response with the slide-roll ratio which depicts a traction curve, the linear shear behavior at the very low shear rate, which is controlled by a elastic property of fluid, and non-linear shear behavior are experimentally estimated. Furthermore, the empirical relationship between the shear stress and shear strain is formulated.

Isoviscous-EHL and mixed lubrication mechanism of parallel slide-way with oil groove

Abstract The pressure generation of a parallel slide-way with an oil groove is examined experimentally and theoretically. In the experiments, the friction force, floating height and oil film pressure are measured with changing sliding speed, groove intervals and lubricants. The experimental results show that the friction property of the parallel slide-way with an oil groove is dominated by a hydrodynamic lubrication mechanism in high sliding speed condition and in mixed lubrication condition. Oil pressure generated at the entrance from the groove to the sliding surface and elastic distortion of the slider are taken into consideration in calculating the oil film pressure generation. The calculated results show that the slider is distorted elastically and forms a micro wedge, and consequently a sufficient load carrying ability is generated. The measured oil pressure distribution resembles the calculated pressure distribution.

Development of Hybrid Magnetic Spindle —Characteristics of Test Spindle—

The hybrid magnetic spindle for the machining center has been developed. In this report, the relationship between the characteristics of test spindle and the PIDs coefficients as well as the charging pressure of the air bearing is investigated. The amplitudes of whirling of the test spindle are also measured at various rotating speeds. As a result, the advantage of the hybrid magnetic spindle is specified.

Study on work regenerative chatter in cylindrical plunge grinding of low stiffness workpiece.

This paper deals with the analysis of work regenerative chatter in cylindrical plunge grinding of low stiffness workpiece. The effect of grinding parameters on chatter stability and chatter frequency is discussed in some experiments and a theoretical analysis. The chatter stability is examined experimentally by an angular grinding which is a high efficiency grinding method, and it is analyzed to first approximation by the application of the regenerative chatter theory for usual plunge grinding. Dynamic grinding force due to the relative penetrating velocity of the grinding wheel to the workpiece is considered in this chatter theory. The following conclusions are obtained. (1) To increase the structural stiffness results in low chatter stability with the lower stiffness of the workpiece. (2) The chatter theory for usual plunge grinding does not matter in a practical application to the chatter stability analysis in cylindrical angular grinding of the low stiffness workpiece. (3) Plunge velocity scarcely affects the chatter frequency.