Published papers

セラミックスの研削加工において，センサを用いて加工面に生じる異常を実時間検知できれば，不良品の早期発見やプロセス改善につなげることができる．本研究では，センサデータの解析手法として，加工状態可視化マップを提案した．センサデータを加工位置に対してマッピングすることで，工作物表面への影響を視覚的に捉える手法である．可視化マップと工作物の表面プロファイルの関係を調べ，その有効性を確認した．

This investigation reports the physical characteristics of electrorheological (ER) gels, which are a type of functional material having controlled surface friction. We previously developed slip clutches using ER gels sandwiched between electrodes, and verified their responses and controllability. We newly report the temperature and shear rate characteristics of ER gel in this study because the input and output electrodes of the clutch continuously slip past each other. While the temperature of ER gels increased when energized, the shear stress hardly changed. Instead, wearing and adaptation to the electrode affect the property. The shear rate hardly affected the shear stress in the high-shear-rate region. Conversely, the shear stress depended on the shear rate in the lower region.

The three-dimensional CO2 dissolution process through a gas-liquid interface in microfluidic devices was investigated experimentally, for the precise control of CO2 dissolution. The gas dissolution was evaluated by using confocal micron-resolution particle image velocimetry (micro-Ply) combined with laser induced fluorescence (LIF), which has the ability to measure the velocity and dissolved CO2 concentration distribution in a liquid flow field. The measurement system is based on the confocal microscope, which has excellent depth resolution and enables visualization of the three-dimensional distributions of velocity and dissolved CO2 concentration by rendering two-dimensional data. The device is comprised of a polydimethylsiloxane chip, whose microchannels were fabricated by using a cryogenic micromachining system. The width and depth of the liquid flow channel are larger than those of the gas flow channel. This is due to the need for decreasing the width of the gas-liquid interface and increasing the hydraulic diameter of the liquid channel, whose conditions generate a static gas-liquid interface. The experiments were performed for three different liquid flow conditions corresponding to Reynolds numbers of 1.0 x 10(-2), 1.2 x 10(-2) and 1.7 x 10(-2), and the gas flow rate was set to be constant at 150 mu L/min. The LIF measurements indicate that an increase in the Reynolds number yields a decrease in dissolved gas in the spanwise directions. Furthermore, molar fluxes by convection and diffusion were evaluated from the experimental data. The molar fluxes in the streamwise direction were at least 20 times as large as those in the spanwise and depthwise directions. This reveals that an increase in momentum transport in the spanwise and depthwise directions is an important factor for enhancing mass transfer in the gas-liquid microchannel flow. (C) 2012 Elsevier Ltd. All rights reserved.

Microfluidic chips with micro- or nanoscale channels are currently in great demand. PDMS (polydimethylsiloxane), a viscoelastic polymer, has high transparency and good chemical stability, making it a suitable substrate material for such chips. However, it is difficult to machine PDMS by conventional cutting processes because of its high elasticity and adhesion. We proposed the cryogenic micromachining of PDMS completely immersed in liquid nitrogen as a direct process to fabricate customized 3D nano/microfluidic chips precisely. In this study, the feasibility of ultra-precision cryogenic machining is studied as an extended nanofabrication process. (C) 2012 CIRP.

ER gel is a relatively new type of functional material. The surface of ER gel has a shear stress characteristic, which increases according to the applied electric field. Introducing the gel into interface elements of a force transmission system realizes functional clutches and brakes. This study aims to develop a linear actuator that is safe, can operate in reverse, and can generate a large force using such a functional clutch. Applying an ER gel clutch in a force transmission system decreases inertia and the mechanical limits of the maximum speed while not limiting controllability. Such properties contribute to a high level of safety. This article reports, in particular, on stabilizing the output of the linear actuator.

Electro-rheological Fluid (ERF) is the functional fluid that can change its viscoelastic property by applying electric field. However, ERF shows the sedimentation of the ER particles in long time use, and it caused the unstable ER effect. The Gel-structured ERF (ERG) has been developed to solve this problem. When a metallic flat plate is placed on the ERG sheet, ERG shows the high shear force due to the occurrence of the contact between the gel and the plate in response to the applying electric field (ERG effect). ERG effect can be obtained not only for metallic materials but also non-metallic materials by applying the one-sided electrode, and the ER effect is supposed to be considerably influenced by the material and geometrical properties of flat plate on the ERG sheet. In this study, the influences of the material and geometrical properties of sliding plate are experimentally analyzed from the viewpoint of the relative permittivity, surface roughness and flatness, and the design instruction for the selection of materials and their geometrical issues are proposed.

This paper deals with axial ultrasonic vibration-assisted machining with workpiece bending. It was proposed as a novel machining method for the reduction of the chippings at the machined holes during micro through-hole drilling of chemically strengthened glass. In micro through-hole drilling of chemically strengthened glass, machining accuracy and efficiency tend to be low because the material's high hardness and brittleness cause rapid tool wear and large chippings at the inlet and outlet of the machined holes. In order to machine small holes with high accuracy, the reduction of the tensile stress that causes large chippings at the outlet of the machined holes is an issue of primary importance that deserves investigation. In the proposed machining method, the glass plate is bent slightly to be convex upward through the application of a compressive stress at the posterior surface of chemically strengthened glass, with a specially designed jig. Using this proposed method that can reduce the tensile stress, the chipping size at the outlet of the machined holes was successfully reduced with applied compressive stress values of 38.9 MPa. In conclusion, it has been clear that the axial ultrasonic vibration-assisted machining with workpiece bending has the potential for achieving high-precision and high-efficiency machining for chemically strengthened glass.

4K and 8K technologies are attracting attention in optical industries. The most important mechanical element to enhance the imaging performance is the aspherical lens requiring higher surface quality and higher form accuracy. Currently, the production process of optical lenses consists of brittle-mode grinding and pro-longed polishing process, which play a role of shaping the form and producing the fine surface, respectively. However, this process is not considered to be suitable for manufacturing such higher-quality lenses for 4K and 8K imaging devices because a required form accuracy could not be ensured, and the polishing time gets longer. To enhance the form accuracy and production efficiency, application of ductile-mode grinding is expected to reduce polishing amount. However, the shape error generated by the ductile mode grinding is not clear. Therefore, the purpose of this research is to analyze the relation between the shape error and the grinding force estimated from motor-current in the grinding machine. The motor-current acquisition system in all translational axes and the work spindle is constructed and implemented into a 4-Axis ultraprecision aspherical machine. The grinding force in each axis is derived by subtracting the motor current during non-grinding previously obtained in air-grinding test from the current during grinding. Firstly, the behavior of the motor current in each axis is investigated from the viewpoint of repeatability and position dependency. While the periodic fluctuation of the motor current affected by the influence of permanent magnet in the linear motor is confirmed, it shows high repeatability at each position. This result indicated that grinding force is easily calculated from the motor current with less uncertainty. Then, influence of grinding condition in the range of ductile mode grinding on the shape error is analyzed by monitoring the motor current. Toward the outside of the workpiece, the shape error gradually increases with the increase of motor current, which means larger grinding force at the outer side causes the deformation of the resin grinding wheel.

The demand for optical glass lenses is rising owing to the increase in image resolution. Optical glass is a hard and brittle material. Thus, an efficient and precise grinding method is required for optical glass to improve lens quality and productivity. There are a few methods of producing crack-free machined surfaces; however, they provide only limited grinding efficiency. To resolve this issue, the authors’ group has proposed the reaction-induced slurry-assisted (RISA) grinding method, which expands the range of ductile-regime grinding by utilizing the chemical–mechanical action of a cerium oxide slurry. In this study, the grinding performance of RISA grinding is experimentally evaluated for different pH levels. The results are compared using Tukey’s test, where surface roughness is considered as the characteristic value and the pH value as the analyzed factor. The result shows that RISA grinding efficiently produces a high-quality surface when the slurry is alkaline. The adhesion of cerium oxide abrasives to the wheel in RISA grinding follows the same mechanism as slurry aggregation. In addition, adhesion is more likely to occur when the alkalization of the slurry promotes aggregation. The tank in the slurry supply unit is replaced with a rotating tank to ensure stable RISA grinding with a highly aggregable slurry while preventing aggregation. The performance evaluation shows that a high-quality surface with a surface roughness of less than 10 nm in most parts is obtained. Moreover, the critical depth of cut stably increases by a factor of 5.8.

Machining of steel-based alloy (STAVAX) and tungsten carbide (WC) is very challenging due to their superior hardness. Severe wear in the machining of the die materials is the dominant problem. Texturing on the rake face of the tool and ultrasonic elliptical vibration cutting (UEVC) may resolve this issue and could prolong tool life. The patterns on the rake face of the tool entrap the chip and debris created in machining and prevent abrasion. During UEVC the flank face of the tool does not contact the workpiece and the rake face of the tool helps the chip evacuate from the machining area when the tool disengages with the workpiece. Thus, UEVC reduces cutting force and tool wear compared to conventional cutting. This paper investigates the cutting performance and tool wear in machining of the die materials with textured polycrystalline diamond (PCD) tools under UEVC. The linear patterns parallel or perpendicular to the chip flow are engraved on the rake face of the PCD tools with the focus ion beam (FIB) process. Orthogonal cutting experiments are carried out on ultra-precision machine tools with and without UEVC. Machining under UEVC remarkably reduces the cutting and thrust force and improves tool life. For machining of STAVAX with the textured PCD tool, the linear patterns alone do not improve the cutting, but they improve the cutting when they are combined with UEVC. In machining of WC, the linear pattern becomes effective by slightly decreasing the thrust force and friction coefficient when UEVC is not applied.

Machining of mold steel like STAVAX is still challenging due to significant tool wear. The ultrasonic elliptical vibration cutting (UEVC) that enables dramatic reduction of cutting force is considered as a potential solution. Tool-texturing on the rake face to reduce the friction coefficient between chips and the tool can be another solution as well. Hence, combining these two approaches may provide synergetic effect to further reduce the cutting force. In order to understand this effect, chip formation using these approaches is experimentally investigated. Chip morphology is totally different whether to use UEVC and textured tools. It was shown that the perpendicular pattern to the chip flow direction may enhance the chip-lifting effect during UEVC. Thus, upward force is applied to the workpiece, which causes reduction of thrust force.

Although advanced manufacturing strategies such as Industry 4.0 are becoming popular, many small and medium-sized enterprises (SMEs) are still facing challenges in factory automation. One of the reasons is that factory automation may require significant system updates. A retrofittable system that handle versatile tasks is needed to facilitate easier integration in the manufacturing industry. This paper proposes a system that can assist multiple numerical control (NC) machine tools using an autonomous mobile robots (AMR). The tasks integrated are chip removal inside the NC machine tool's chuck, vibration analysis while the NC machine tool is processing and charging AMR. AMR has to perform these tasks within the production line's strict time constraints and AMR's battery constraint. The proposed system produced a feasible schedule of the tasks. Numerical simulation evaluated the feasibility of the produced schedule. The produced schedule was verified by performing in the real world.

Optical microcavity, which can localize light at a certain spot for a short period of time, has a wide range of applications, such as optical signal processing and optical frequency combs. Single crystal CaF2 has excellent optical properties and many research on the manufacturing process to create a microcavity has been done. However, due to its unstable thermal conditions, stable oscillation of Kerr comb could not be done. Single crystal MgF2, which also has excellent optical properties, has stable thermal conditions suitable to create a microcavity. Like CaF2, MgF2 microcavity can only be manufactured by ultra-precision cylindrical turning, yet its appropriate processing conditions is not known. In this study, a method to derive the critical depth of cut theoretically in ductile mode machining was proposed in consideration of specific cutting energy, mechanical properties and slip system of workpiece, and tool geometry. The critical depth of cut calculated by the proposed method roughly agreed with the experimental value on the MgF2 plane. Unlike CaF2, MgF2 has an optical anisotropy; therefore, in order to create a microcavity where the refractive angle is constant, the resonance part needs to be made on a cylinder with (001) plane as end face. Therefore, a microcavity was fabricated according to the critical depth of cut on a cylinder with (001) as end face derived from the proposed method, and the surface integrity was evaluated from the viewpoint of microcavity performance.

High-speed directed energy deposition (DED) offers advantages such as efficiency, thin coating layers, and reduced heat-affected zones, making it ideal for repairs and coating on existing parts across various industries. In the DED process, various deposition parameters are included and affect the thermal history. Moreover, a thermal history significantly affects the deposit's mechanical properties by varying metallographic structure. Therefore, thermal simulations of DED are highly demanded due to the time and cost challenges associated with experimenting across different process parameters. However, thermal simulations of DED have difficulties because of the process by which material and heat source are supplied from time to time to the melt pool. Many studies have been conducted on thermal simulations of DED, however, few studies focus on high-speed DED coating. Therefore, this research develops the thermal simulation techniques for high-speed DED coating by exploring five simple methods for element addition and heat input. The geometry of the workpiece model was simplified to reduce the simulation cost. Using the Ansys Parametric Design Language (APDL) software and the simplified workpiece model, we conducted thermal simulations and validated them against experimental data acquired from high-speed imaging and two-color temperature measurements. Through these methods, the study proposed the temperature comparison method of experiment and simulation results and identified the suitable method for element addition and heat input in high-speed DED coating that closely replicates the actual temperature within the coating layer. This method reduces the need for finer mesh, effectively lowering computational costs while maintaining accuracy. The findings provide insights into practical simulation practices for DED and contribute to enhancing parameter validation in additive manufacturing simulations, supporting further development in high-speed DED coating technology.

In this paper, we propose cutting-force-estimation method for a ball-screw-driven system using triple inertia model. In many cases, dual-inertia model is applied to describe the dynamic behavior of the ball-screw-driven system. In this paper, triple-inertia model is applied and cutting force was estimated without additional sensors, such as dynamometer. The cutting force observer is designed, regarding the ball-screw-driven system as two input and three output system. Simulation results indicate that the proposed method enables accurate estimation around the resonance frequencies. Experimental results showed that the proposed method could monitor external force without being interrupted by the inertia forces.

Disturbance observation is a sensorless process monitoring technique that has not yet been applied to the monitoring of tool collision in the use of machine tools. This paper presents a monitoring algorithm that detects collisions that involve the breakage of drills through observation of the disturbance force change rate. A comprehensive experimental study of diverse operator-induced collisions was conducted to analyze the collision detection potential of the disturbance observer. It was found that collision monitoring by the disturbance observer is more sensitive and responsive than that using a sensorless jerk observer. © 2014 CIRP.

Detection of a tool fracture is necessary to ensure cutting accuracy and to avoid a tool breakage because tool fracture is one of the significant prediction signals of the tool breakage. For monitoring the tool condition, generally additional sensors are used. However using these sensors causes high cost and increase of failure rate. In this paper, a novel sensor-less detection method of tool fracture in drilling process is proposed on the basis of a disturbance observer theory. It is applied to the x-y stage of the machine tool. The proposed method requires no external sensor because it uses only the servo information of the spindle control system. Since structures of normal drills with two floats are symmetrical with respect to a point, theoretically the cutting force in the x and y directions does not work. When the drill is fractured, its structure becomes asymmetry so that unbalanced forces would exert in the x and y directions at intervals of the spindle speed. Therefore, it is possible to detect a tool fracture by the frequency analysis of estimated disturbance force with a wavelet transform. The experimental results show that the proposed method is available for detection of the small tool fracture effectively.

The automation of machining processes requireshighly accurate process monitoring. However, the use of additional sensors leads to a significant increase in the cost and reduces the stiffness and reliability of mechanical systems. Hence, we propose a system called the cutting force observer, which uses a sensor-less and real-time cutting force estimation methodology based on the disturbance observer theory. Monitoring methods using the cutting force observer may enhance the productivity during turning. One of the parameters that significantly affect the cutting process is the shear angle. The determination of the shear angle is very important as it can be used for identifying the machining conditions. In this study, an external sensor-less monitoring system of the shear angle during turning is developed, and its performance is evaluated.

Polydimethylsiloxane (PDMS) is difficult to machine by conventional cutting process because of its low elasticity and high adhesion. We proposed the cryogenic micromachining method assisted by liquid nitrogen cooling for direct fabrication of 3D micro channels on PDMS substrate in short time. In this paper, the cryogenic cutting mechanism is clarified through some verification experiments. Moreover, Pre-Deformation-assisted Cryogenic Micromachining (PDCM) method is also proposed for fabricating the unique shapes of channels and its validity is evaluated experimentally. The results of cutting tests show that 3D unique micro channels can be processed precisely and rapidly on PDMS.

Aerostatic guideways have been applied to precision machine elements. Recently, downsizing and the increased use of high-density technology in IT devices have generated demand for higher accuracy in aerostatic guideways. It has been pointed out that the micro-bounce occurs when the slider passes over the aerostatic guideway with small pores. This transient state micro-vibration decreases the accuracy of aerostatic guideways and, thus, it is now expected to be suppressed. The purpose of this study is to analyze the micro-bounce mechanism of aerostatic guideways caused by pores, and to propose new designs for the suppression of micro-bounce. (C) 2009 CIRP.