Published papers

Carbon fiber reinforced plastic (CFRP) is used in machine tool components to provide high specific stiffness with high damping properties and low thermal expansion; further, it is combined with metals in specific ratios to enable the use of existing equipment and machine design. The development of CFRP spindle shafts has design flexibility in the stacking sequence. The improvement and analysis of spindle unit dynamics are essential for achieving high productivity in machining, and prediction methods for dynamic stiffness with lower computational costs are required to estimate and optimize the machine performance of the design proposals. Therefore, parameter identification for the equivalent physical properties of composite materials with CFRP and steel was proposed in this paper to use general solutions for a one-dimensional Timoshenko beam model. Four different analytical models of the CFRP spindle shaft following the actual development phase were designed via generalized receptance coupling to multi points in order to observe the model shapes. The frequency response functions and mode shapes of the spindle shaft models were compared with those of finite element methods and impact tests. The spindle shaft model reflecting the applicable location of CFRP in the rotational axis demonstrates a sufficient estimation accuracy for natural frequencies and mode shapes. The spindle shaft model reflecting the stacking sequence demonstrates robustness against the parameterization errors of the CFRP. A motorized CFRP spindle unit was modeled by combining a spindle shaft model and bearing models; the bearing dynamics were experimentally studied under heat radiation after stopping the spindle rotation. Moreover, a steel spindle shaft model and several types of CFRP layout with the same dimensions were compared on the spindle unit model; the CFRP spindle unit yielded a greater dynamic stiffness. The layout of the CFRP application and requirements on manufacturing are discussed for the further improvement of the dynamic stiffness.

In this study, Electro-Adhesive Gel Sheet (EAGS) was fabricated. It is suggested that the electrical resistance characteristics of EAGS could be applied as slip detection sensors or contact detection sensors. EAG is a functional elastomer which can change surface adhesiveness depending on an electric field, and EAGS is a sheet of EAG fabricated on a flexible electrode sheet. It was found that slipping on the surface when grasping an object or contact with a grounded conductor changes the resistance inside the EAGS, and the mechanism was analyzed from an engineering point of view.

We detail a dispersion engineering strategy for microresonators allowing us to generate microcombs in the near-infrared and mid-infrared regimes, and identifying optimal shapes for achieving anomalous dispersion suited to different wavelength regimes.

We detail a dispersion engineering strategy for microresonators allowing us to generate microcombs in the near-infrared and mid-infrared regimes, and identifying optimal shapes for achieving anomalous dispersion suited to different wavelength regimes.

The buffing process for finishing an automobile's body is still done manually, and the final surface quality of the body depends on the skill and technique of the worker. To automate buffing, not only tool path control but also precise and fast force control is required. In this study, a novel methodology based on the sensor-less force control technique and the quarry matrix capable of the mode decoupling is proposed for a parallel mechanism polishing machine to control x-y trajectory, tool posture, and polishing force in z-direction, and its validity for automated buffing is verified. (C) 2013 CIRP.

Intelligent machine tool is required to implement highprecision process monitoring for judging the abnormal tool conditions. Various techniques have been widely researched and studied to maintain machine tool in good condition and to detect tool wear. The occurrence of tool wear can be detected by monitoring the cutting torque, which is basic information for machining. The purpose of this study was to propose a sensor-less cutting force and torque monitoring method and to develop an intelligent stage using this method.

Nowadays, due to the widespread use of rehabilitation and virtual reality technology, tactile display systems have attracted the attention of researchers from the medical and amusement fields. A clutch mechanism that employs ER and MR fluids is appropriate for force transmission in a tactile display device, because the ER and MR effects are passive and safe for the operator compared with an active actuator using motor. The developed ERG produces approximately 20 times higher shear forces than ER fluid and exhibits stable performance. In this research, an ERG multiple-disk clutch is fabricated and applied to a tactile display system. The experimental results of the control test indicate that the tactile display system with the proposed control method can exhibit the 'sense of touch' of various viscous fluids.

Suppression of chatter vibration is required to improve the machined surface quality and enhance tool life. For monitoring the chatter vibrations, additional sensors such as acceleration sensors are generally used, which results in high costs and low reliability of the machine tools. In this study, a novel in-process method to detect chatter vibrations in end milling is developed on the basis of a disturbance observer theory. The developed system does not require any external sensors because it uses only the servo information of the spindle control system. Self-excited and forced chatter vibrations are successfully detected. (C) 2011 CIRP.

Electrorheological gel (ERG) is a novel functional elastomer, which has frictional and adhesive surface properties that vary according to the intensity of an applied electric field. This peculiar phenomenon is referred to as the electro-adhesive (EA) effect. The shear stress of ERG generated under an applied electric field is approximately 30-40 times higher than that of electrorheological fluids (ERF), due to its high adhesive strength. However, the generated EA effect of ERGs varies widely due to surface conditions, especially the density and distribution of ER particles at the surface. In order to stabilize and improve the performance of ERG, the electrical field-assisted molding process is proposed as a production method. In this process, the mixture solution including ERFs and gel agent is gelling under electric field. The principle of the EA effect is theoretically investigated and a high-performance ERG produced by the proposed process, in which ER particles are aligned densely at the surface, is developed and the performance is experimentally evaluated by surface observation and shear test, revealing a highly dense arrangement of ER particle at its surface and a higher shear stress twice that of conventional ERG.

Electro-rheological gel (ERG) is a functional elastomer, which changes its surface adhesive property according to the intensity of electric field. In this study, ERG is applied to multiple-disk brake element to realize both simplification of structure and wide range of controlled brake torque. First, static performance of ERG multiple-disk brake (ERG-MDB) is evaluated experimentally. It is clear that a generated brake torque depends on an electric field and the number of layer of ERG. ERG-MDB with 6 layers shows 5 times brake torque as high as that with 1 layer. Second, considering the dynamical model of the ERG-MDB, dynamic performance is investigated through the forced vibration test. The result shows that dynamic damping and stiffness coefficients are changed widely according to applied electric field.

Electro-rheological gel (ERG) is a novel functional elastomer whose surface frictional and adhesive property varies according to the intensity of applied electric field. This peculiar phenomenon is named as Electro-adhesive effect. A generated shear stress of ERG under applied electric field is approximately 30∼40 times higher than that of ERF because of high adhesive strength. However, the performances of ERG vary widely due to its surface condition, especially density and distribution of ER particles at the surface. In order to stabilize and improve the performance of ERG, the electric- filed assisted molding process is proposed as the producing method of ERG. In this study, first, the principle of electro-adhesive effect is theoretically investigated. Second, a high-performance ERG produced by the proposed process, in which ER particles are aligned densely at the surface, is developed and its performance is evaluated experimentally. As the experimental result, the high-performance ERG shows twice higher shear stress than the conventional ERG. © 2009 IOP Publishing Ltd.

Large amount of cutting oil consumption is one of the issues for environment. The Minimum Quantity Lubrication (MQL) technique has been applied to the near-dry cutting process. However, MQL technique generates oil mist which is harmful to the working environment and the health of factory workers. In this study, a new lubrication system called Direct Oil Shot Lubrication System (DOS) was developed and applied to milling processes. The performances of DOS technique was evaluated by measuring the floating oil mist and carrying out the cutting tests. The amount of floating oil mist of DOS system was considerably reduced compared to the MQL. The behavior of small oil drops supplied from DOS nozzle to cutting edge was analyzed by means of a high speed video observation, and the optimum setting for DOS was obtained. The experimental result shows developed DOS system realized the smaller density of oil mist floating than the MQL technique while the DOS attained the almost same lubrication effect in milling process as the MQL technique.

Semiconductor process technology increasingly requires high accuracy and efficiency. In the case of processing thin fragile substrate such as silicon wafer, it has to be fixed with low strain. In addition, its fixture device can be used under vacuum condition because some processes are carried out in vacuum. It is required to develop a new fixture device for vacuum transportation of silicon wafer. ERG is the functional material whose friction characteristic varies according to the intensity of applied electric field. The surface friction of ERG can be changed quickly and reversibly applying the electric field. In other words, it becomes easy to fix and release a substrate by control of electric field. In this study, ERG is applied to a fixture element of silicon wafer available for vacuum process. The ERG fixture element was trial-manufactured and its performance under vacuum condition was evaluated experimentally. The result shows that the ERG effect emerges in vacuum and ERG can fix silicon wafer sufficiently. Moreover, numerical analysis of electric filed was carried out to obtain the optimal pattern of the one-sided electrodes used for the ERG fixture element. It is clear that the optimal width of electrodes exists according to the gap of electrodes and the thickness of ERG.

In this study, Electro-Adhesive Gel Sheet (EAGS) was attached to a robot hand and used as a gripper. Electro-Adhesive Gel (EAG) is a functional elastomer which can change surface adhesiveness depending on an electric field. EAGS is a sheet of EAG fabricated on a flexible electrode substrate. It is confirmed that the electrical current flow inside EAGS is changed when the robot hand with EAGS (EA hand) touches a grounded metal object or slips on it. By applying these current characteristics, the applicability of contact detection and slip detection is investigated to monitor gripping status in robot hand. From the results, EA hand can detect not only the contact but also lifting the object from the base plate. Furthermore, slipping can be suppressed by adjusting an applied potential difference of the electrodes according to the slip detection.

To maximize the potential for high material removal rates in simultaneous processes such as parallel milling, developing strategies for successful chatter suppression/avoidance is an important concern for manufacturers. In this study, the effectiveness of the spindle speed difference method (SDM) for chatter suppression is discussed in a parallel end-milling process where a flexible workpiece is machined by two tools rotating in opposite direction. The process model is developed, considering that the dynamic variation due to the regenerative effect occurs on a plane perpendicular to the tool axis direction. Through the process simulations and the experiments, this study provides informative discussion for comprehending the process behavior. Additionally, a real-time active chatter suppression system with adaptive SDM, where the spindle speed difference is sequentially optimized during the process according to the tracked chatter frequency, is developed by integrating a chatter monitoring system based on sensorless cutting force estimation with sliding discrete Fourier transform. The results show that the developed real-time adaptive system of spindle speed suppresses chatter vibrations more effectively than non-adaptive SDM system; hence, the integrated system can contribute self-optimizing machining systems oriented to Industry 4.0.

Electro-rheological fluids (ERFs) are composed of a functional fluid and colloidal suspension. Their rheological properties vary rapidly and reversibly with the applied electric field intensity. ERFs are mixtures of nonconductive silicone oil and inorganic/organic composite electro-rheological particles. Investigations into the properties of ERFs have led to remarkable advances in their performance in recent years. However, ERFs exhibit an undesirable property that obstructs the long-term use of ERF devices, namely the sedimentation and separation of ER particles from the silicone oil. The sedimentation of ER particles reduces the electro-rheological effect. In order to suppress the sedimentation and thereby improve the performance of ERF devices, a new functional material called Get Structured ERF (ERG) is developed and its basic properties are analyzed in this study. The ER particles are sustained in the gel component, and thus will not precipitate out. This suppresses the decrease in ER effect associated with precipitation. The developed ERG shows large shear stress variation in response to the applied electric field. This high performance of ERGs involves a different mechanism than that observed in ERFs. In order to elucidate the mechanism in ERGs, the behavior of ER particles was observed under an electric field. Conditions at the interface between the electrode and ERG were found to change rapidly in response to the applied electric field, resulting in the variation of shear force.

The demand for large aperture lenses with high surface quality and form accuracy used for single-lens reflex cameras has been increasing. Generally, large aperture glass lenses are produced by ultra-precision grinding. Considering the increasing global competition, the grinding process has to be improved. However, highly efficient grinding causes worse surface quality, which leads to much polishing and ultimately results in lower form accuracy. Thus in this study, aiming at the realization of highly efficient and precise grinding of glass lenses, cross grinding of optical glass BK7 is carried out. As a first step of the study, the influence of grinding conditions on the surface quality is investigated experimentally.

The suppression of chatter vibration is required to enhance the machined surface quality and to increase tool life. In this study, a new, conceptually active approach for chatter suppression in machining is proposed. The hybrid control method developed by applying sensorless force control with a disturbance observer enables the simultaneous and independent control of the position trajectory and band-limited forces. The proposed method is introduced to the carriage of a prototype desktop-sized turning machine, and the ability to suppress chatter is evaluated by end-face cutting tests. The results demonstrate that actively controlling a band-limited force leads to the avoidance of chatter. (C) 2014 CIRP.

Smart materials have been developed in many leading technologies. Smart material is a material that gives a specific reaction to the change and stimulus of the external environment such as light, heat and electromagnetic fields. Electro-rheological Gel (ERG) is one smart material. ERG changes its surface adhesive properties rapidly according to the intensity of the applied electrical field. This unique property is named Electro-adhesive effect (EA effect). In this research, as a novel electro-adhesive film which is replaced with ERG, Electro-adhesive film with micro mesh sheets is developed and named EAMS. Furthermore, it is proved that the developed film using the mesh sheet produces the EA effect and that the performance of EAMS is enhanced according to the increase of the open space and the number of layers.

ER gel exhibits various adhesive characteristics according to the applied electric field. This characteristic is called the EA effect. The results of a recent study reveal that the EA effect also occurs in a vacuum. Therefore, it is expected that ER gel can be applied to a chucking or damping device in a vacuum process. However, the characteristics of ER gel in a vacuum have not been sufficiently clarified. The purpose of this study is to experimentally evaluate the characteristic of ER gel in a vacuum. The performance of an ERG fixture element used for a silicon wafer in a vacuum is evaluated through shearing tests. The experimental results indicate that the ER gel demonstrates satisfactory performance in a vacuum. Moreover, the outgas released from the ER gel in a vacuum is evaluated, and the influence of the degassing time on the outgas is investigated.