It is widely known that electrical pitting occurs when an electrical current is passed through a ball or roller bearing. The authors have investigated critical electrical current density causing electrical pitting and have shown that it occurs in a ball bearing even at an extremely low current. In this paper we present the results of an experiment in which a small ball bearing was supplied with a direct current (DC) voltage to determine the voltage required to induce a current. A film of grease acts as the insulator on an antifriction bearing used, and the thickness of this film is an important consideration and the current must pass through this film. Four types of grease were used on the bearing, which was rotated at various speed during 500 hours. A potential of 1.3V to 1.5V was necessary to induce the flow of current. The results indicate that the voltage supplied by typical dry cell batteries is sufficient to drive a currents through a small bearing, and that the experimental conditions had little effect on the magnitude of the flowing current.
Energy distribution ratio into micro EDM electrodes was determined based on the summation between the ratio of energy loss due to heat conduction within electrodes and ratio of energy carried away by debris. Ratio of energy loss due to heat conduction was obtained by comparing the measured and calculated temperature rise on electrode after igniting plural pulses discharges. On the other hand, the ratio of energy carried away by debris was calculated based on the measured removal volume. Energy distribution ratio into micro EDM anode and cathode was between 10% and 15% in total which was comparatively lower than that of macro EDM. This is because much larger fraction of the total discharge energy is consumed for the generation and enthalphy increase of the plasma in the early stage of discharge. Besides, unlike macro EDM the energy carried away by debris in micro EDM cannot be ignored compared with the energy lost due to heat conduction. This means, the energy consumption by material removal in micro EDM with regard to the energy distributed into the electrodes is more efficient compared to that of macro EDM.
Process damping in metal cutting is caused by the contact between the flank face of the cutting tool and the wavy surface finish, which is known to damp chatter vibrations. An analytical model with process damping has already been developed and verified in earlier research, in which the damping coefficient is considered to be proportional to the ratio of vibration and cutting velocities. This paper presents in process identification of the process damping force coefficient derived from cutting tests. Plunge turning is used to create a continuous reduction in cutting speed as the tool reduces the diameter of a cylindrical workpiece. When chatter stops at a critical cutting speed, the process damping coefficient is estimated by inverse solution of the stability law. It is shown that the stability lobes constructed by the identified process damping coefficient agrees with experiments conducted in both turning and milling.
The application of light-weight drive technology into the lithography stage has been the current state of art because of minimization of power loss. The purpose of this article is to point out the so-called, "surface stage" which is composed of Lorentz forced 3 DOF (Degree Of Freedom) planar motor (x, y and theta z), air levitation (bearing) system and motor cooling system, is the most balanced concept for the next generation lithography through the verification of each component by manufacturing simple parts and test stand. This paper presents the design method and procedure, and experimental results of the air levitated surface stage which was conducted several years ago, however the author is convinced that the results are enough to adapt various developments of precision machining tool.
We developed a three-phase electrostatic stepper micromotor and performed a numerical simulation to improve its performance for practical use and to optimize its design. We conducted its circuit simulation by simplifying its structure, and the effect of springback force generated by supported mechanism using flexures was considered. And we considered new improvement method for electrodes. This improvement and other parameter optimizations achieved the low voltage drive of micromotor.
This paper describes single-point incremental micro-forming of miniature shell products 50 µm to 1000 µm in size. First, the conditions of the micro-forming of a pyramid with a 1 mm square base were optimized to cause large elongation of a blank up to 128%, resulting in a tall pyramid with an elevation angle of 64°. Next, the influence of the tool rotational speed on the forming limit in forming a pyramid with a 50 µm square base was investigated. It was found that the optimum rotational speed decrease with the size of a pyramid. Finally, letters and numbers 100 µm to 500 µm in size were formed as free form products. The effect of grain size on the miniature shell products was discussed based on the results and it was concluded that the effect must be taken into consideration in micro-forming processes of miniature products smaller than 100 µm in size as far as the grain size is not very small as compared with the size of a product.
This paper proposes a closed-loop identification method based on an AC servo control system for permanent magnet synchronous motor (PMSM) parameters. The parameters include the inductance of the quadrature-direct axis, resistance of the stator, and magnetic flux linkage of the rotor. First, the nonlinear factors influencing the parameter identification accuracy—the motor model error caused by non-sinusoidal flux, switch dead zone of the inverter, and rotor position feedback delay of the encoder—were analyzed to develop corresponding compensation methods. Second, an experimental system was developed, and the proposed method was implemented and evaluated. The analytical and experimental results showed that the identified inductance-current curve was consistent with the results of finite element analysis after compensation, while the estimated resistance and flux were closed to the measured values. These results confirm the validity of the proposed method.
Since variations in tooth flank form among the teeth of a gear are one of the primary causes of noise and vibration in gear systems, the effects of these variations should be analyzed. In the present paper, a simulation program is proposed in which variations in tooth flank form among the teeth of a gear are considered. The effect of different surface finish methods on gear vibration was analyzed using the developed program. The effects of periodic change of profile and helix slope deviation on the vibrational excitation were also examined. The concept of potential gear noise, which is a noise to express directly the effect of tooth flank form of gear on the gear noise, is proposed and a sensory evaluation method is also proposed to evaluate sound level, noise quality and noise uncomfortness. Sensory evaluation result shows that, even if the gears manufactured by different grinding methods have the same tooth flank form macroscopically, they make a large difference in terms of noise quality or uncomfortness because microscopically, the tooth flank form is different among grinding methods. It can be concluded that the proposed sensory evaluation method of potential gear noise could enable gear designers to experience directly the effect of tooth flank form on the noise quality.
Orbiting EDM has the advantages of superior machining quality over static EDM due to advanced flushing. However, improper tool correction to the relative motion in orbiting EDM will result in dimension errors of the product. As features vary in morphology, tool design for orbiting EDM is a challenging task, particularly for mould comprises assorted features. A strategy for correcting the orbital motion to the tool shape is proposed in this study. Effect of different orbital types to the feature's shapes is discussed from its geometrical point of view. This method also applies for orbiting automation by utilizing feature recognition to identify features inside a CAD model and recommends the corresponding orbiting pattern for all detected features. The shaped tool created with this method is capable of fabricating a complex mould precisely. More than 20 different features with different orientations to the machining axis have been tested to accommodate real designs in mould industries.
Demands for measurement of three dimensional (3D) micro-geometries over a large area have recently increased in a variety of industries. In order to meet such requirements, it is necessary to realize a novel coordinate measuring machine (CMM) with a three-dimensional nano-motion system which has high resolution, high response and large measuring area. In this study, a three-dimensional nano-motion system was developed for a scanning probe microscopy (SPM) based CMM with nanometer spatial resolution. The system developed is composed of an X-Y planar nano-motion table system driven by voice coil motors (VCMs), a Z axis nano-motion system driven by a hybrid actuator and a probe holder that equipped with SPM probes. Performance evaluation results confirm that the system simultaneously achieves a long travel range, a high positioning resolution and a high stability.
In order to obtain basic information on the improving the surface integrity of machined surfaces, the relationship between the residual stress of cut surfaces and the cutting edge shapes of cutting tools was examined. Dry facing on a lathe was performed with cutting tools that had various nose radiuses and cutting edge roundnesses. The residual stresses of the cut surfaces were measured by X-ray diffraction method. The results obtained are as follows. When the rake angle was about zero degrees, it found that the nose radius barely affected the residual stresses of the cut surfaces. However, when the negative rake angle was large, the nose radius significantly affected the residual stress. The residual stresses of the cut surfaces shifted compressive side when there was an increase in cutting edge roundness. The residual stress of a cut surface is kept in a high compressive state even though the cutting force decreases greatly due to grinding removing the rake side part of the cutting edge roundness.