Abstract: Thermal errors are important sources of positioning errors in precision machines and are more and more becoming determining factors to meet increasing specifications. In this paper, thermal modal analysis is used to study and reduce the transient thermal displacement errors in precision machines. The temperature decomposition and the thermal displacement field decomposition by thermal modal analysis are derived. The reduction of transient thermal errors by adding additional heat loads is analyzed and the results of two different methods are compared.
Abstract: Recently, compact machine tools have witnessed increased demand in the manufacture of small parts with high accuracy. However, miniaturization of these machines poses problems such as decrease in the accuracy and the range of motion. We focused on miniaturizing a parallel link manipulator, which is known to have high rigidity and accuracy. A non-cylindrical link was adopted in the designed manipulator for avoiding collisions among links with an impact drive actuator attached to their side. We confirmed through repeatability measurements that the developed manipulator had sufficient accuracy for handling small electronic parts.
Abstract: Parallel kinematic mechanism (PKM) is applied to machine tools and robots since its flexibility and speed. In machine tools, additionally, motion accuracy is strongly desired. Although various research works aimed to calibrate static geometrical deviations of the PKM machines in order to improve motion accuracy, influence of dynamic motion error of servo system has not been investigated well up to now. In this study, the influence of servo characteristics on motion accuracy of a PKM machine tool driven by six servo motors is discussed, because it is expected that the contouring motion accuracy of a PKM machine tool is strongly depends on the servo characteristics. A servo motor which installed to the machine is modeled to simulate the motion characteristics of each servo motor. The motor models are coupled with a model of link mechanism, and the motion accuracy of a tool center point is simulated. Also, both of positional and angular errors are simulated successfully. As the results of the simulations, it is clarified that the motion accuracy is strongly depends on the servo characteristics and location of the tool center point. In addition, the motion errors are observed as six dimensional errors. It is also discussed that the influence of friction torques on the motion accuracy.
Abstract: Micro-aspheric lenses molded by micro-aspheric ceramic molds are increasing in the optical systems such as digital cameras and blu-ray players. To finish the molds with high accuracy and low surface roughness, in this paper, the micro-aspheric mold made of Electroless nickel plating are polished by using the newly developed 5-axis magnetostrictive vibration-assisted polishing machine. The magnetostrictive vibrating polisher generates a lateral vibration at 9.2 kHz with amplitude of 30 μm. The polishing pressure is controlled by a balance adjustment mechanism and the polishing load is controllable within a range of 2 mN ~ 20 mN with a resolution of 2 mN. The motion resolution of the X-Y-Z table is 0.1 μm in each direction. The C-axis rotary table is mounted on a B-axis tilting table and the workpiece is mounted on the C-axis rotary table with a vacuum chuck. According to the polishing experiments, the form accuracy was improved to 200 nm P-V and the surface roughness was reduced to 10 nm Rz (1 nm Ra).
Abstract: In laser beam cutting and laser piercing process, the machining speed and quality are very sensitive to the flow of assist gas and laser beam focusing position. In order not only to improve the cutting speed and the removal capability of the molten material and to save the consumption of the gas flow in laser beam cutting, but also to realize high speed piercing of high aspect-ratio holes, a magnetic-levitated (maglev) lens driving actuator was proposed and fabricated. The actuator can drive the lens to achieve real-time positioning control of the relative radial displacement between the lens axis and the assist gas jet nozzle axis (off-axis control) in radial directions in a range of ±1mm within 1.5 μm of tracking error and bandwidths more than 150Hz, and to achieve real-time positioning control of laser beam focusing point in axial direction in a range of ±5mm within 3 μm of tracking error and bandwidth more than 100Hz.
Abstract: In this paper, the improvement of performance design for mass production are shown by using statistical tolerance index Cpk and Cc. Recently, the demand for product performance is getting higher. Meanwhile, precision machining and measurement are also developing in manufacturing industry. To satisfy consumer in terms of product performance, we have proposed advanced tolerancing method by using statistical tolerance index (STI). In this study, it is assumed that the performance of each product can be quantified and depends on the only functional dimension. It is also assumed that the dimension distribution of each machined part follows normal distribution. Consequently, performance of mass production can be quantified statistically. To control performance, we introduce STI which is composed of process capability limitation. After all, performance design is to calculate STI so as to satisfy the demand for performance. There are two problems in performance design. One is a synthesis of STI and another is an allocation of STI. These problems are just like the conventional tolerance synthesis and allocation problems. In this paper, the former problem is formulated algebraically.
Abstract: Thin film patterning by a lift-off method is effective from the viewpoint of cost performance and environmental issues. As a solution to the problems of conventional lift-off methods, the inversely-tapered resist profile with interstice was proposed and its fundamental feasibility was experimenatally proved. The resist profile still needed to be designed properly to solve the problems completely, and therefore a design method was also suggested. The method presupposes that conditions of deposition process have been already determined. However, actually, the conditions relate closely to the design of resist profile and wrong conditions may result in undesirable or infeasible design result. This paper proposes an integrated design method of the thin film patterning process considering design of both resist profile and deposition conditions.
Abstract: Diamond-like carbon (DLC) film has various micro-size defects like pinhole, void and particle. When DLC film is exposed to white light, light is scattered in all direction at defects in DLC film. In this paper, defects in DLC film are detected by observing scattering light from defects under dark-field microscope. DLC film has wavelength dependence of transmittance. Therefore, using its wavelength dependence allows to separate surface and inside defects of DLC film. This paper describes development of bulk defects detecting system using optical filtering and scattering light detecting. Bulk defects of DLC films were successfully separated into surface defects and inside defects. This detecting method of defect is nondestructive and easy, and applicable to DLC films as well as other coating films.
Abstract: Among the major interests in powertrain development are the reduction of frictional losses and service life extension from improved wear resistance. Surface finishing and deterministic microstructuring have been shown to be effective methods in improving the tribological properties of sliding contacts such as bearings and cylinder liners. This is due to their acting as micro pressure-chambers and as wear debris traps. In this work, tribometric ring-on-disc tests were performed in order to evaluate the influence of surface structure − namely, the microstructure geometry and layout − on the frictional behavior of lubricated surfaces. The material combination bronze against steel as typically used in powertrain applications was investigated. The surface structures where machined using electrochemical machining by closed electrolytic free jet (Jet-ECM). It was determined that microstructuring reduced the friction coefficient by up to 45 % in the hydrodynamic regime under loads and speeds found in automotive components. The friction measurements showed that microstructures with low aspect ratios result in the least friction. In addition to the tribological investigations, the process capabilities and implementability in serial production of two surface microstructure fabrication processes: Jet-ECM and a newly developed, hybrid roller micro-embossing and burnishing process were evaluated and contrasted. It was shown that both fabrication methods can attain high structure quality.
Abstract: Tribological properties of copper based porous alloy with penetrated micro size graphite layer were evaluated using a ring on disc testing apparatus in dry condition. A shot peening treatment was applied to ensure the dimple for the graphite penetration. Specimens with various area fraction of the graphite layer were prepared. It was found that the friction coefficient and the wear loss decreased with the increase in the area fraction. However, the decrease of the friction and the wear loss became smaller at excess graphite area fraction.