Yasuhiro Kakinuma

Evaluation methodology of gas permeable characterization in a polymer-based microfluidic device by confocal fluorescence imaging

The evaluation technique of gas permeable characterization has been developed for an increased efficiency of gas–liquid chemical reactions and high accuracy of environmental diagnosis. This technique enables us to measure spatial distributions of velocity and dissolved gas concentration by utilizing confocal micron-resolution particle image velocimetry combined with a laser-induced fluorescence technique. Microfluidic devices with gas permeability through polymer membranes are composed of a cover glass and a polydimethylsiloxane (PDMS) chip with the ability to permeate various gases, since PDMS is an elastomeric material. In the chip, microchannels are manufactured using a cryogenic micromachining system. The gas permeation is dominated by several factors, such as the gas and liquid flow rates, the membrane thickness between the gas and liquid flow, and the surface area of the membranes. The advantage of the present device is to realize the control of gas permeability by changing the surface roughness of PDMS, because the cryogenic micromachining enables us to control the surface roughness of microchannels and an increase in roughness yields an increase in the surface area of membranes. The experiments were performed under several conditions with a change in the gas flow rate, the PDMS membrane thickness and the surface roughness, which affect the gas permeation phenomena. The spatial distributions of velocity and dissolved gas concentration were measured in the liquid flow fields. The results indicate that the velocity-vector distributions have similar patterns under all experimental conditions, while the dissolved gas concentration distributions have different patterns. It was observed that the gas permeability through PDMS membranes increased with an increase in gas flow rates and surface roughness and with a decrease in membrane thicknesses, which is in qualitative agreement with membrane theory. The important conclusion is that the proposed technique is suggested to have the possibility of evaluating the characterization of gas permeable microfluidic device through membranes.

Buffing Performance Analysis of Viscoelastic Polymer with Sensor-Less Polishing Pressure Control

Viscoelastic polymer with high scratch resistance has been developed for coating material of product. Due to some particular characteristics such as viscoelasticity, it is difficult to finish the polymer coated surface. In the present circumstances, its polishing process is carried out by the trained technician and depends on the skill like adjustment of the polishing pressure according to the situation. To realize automation of the polishing, high-precision and highly-responsive force control is required firstly. Typically force control is done with force sensor. However when external sensor is used, there are some problems such as high-cost, reduction of machine stiffness and thermal drift. The thermal drift which is caused by polishing heat prohibits accurate measuring of force. The purpose of this research is to develop the polishing pressure control method without any additional sensor. In addition, applying the control method to buffing machine, buffing performance of viscoelastic polymer is experimentally analyzed.

Stabilizing output of an electrorheological gel linear actuator

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.

Bi-material crystalline whispering gallery mode microcavity structure for thermo-opto-mechanical stabilization

We fabricated a calcium fluoride (CaF2) whispering gallery mode (WGM) microcavity with a computer controlled ultra-precision cutting process. We observed a thermo-opto-mechanical (TOM) oscillation in the CaF2 WGM microcavity, which may influence the stability of the optical output when the cavity is employed for Kerr comb generation. We studied experimentally and numerically the mechanism of the TOM oscillation and showed that it is strongly dependent on cavity diameter. In addition, our numerical study suggests that a microcavity structure fabricated with a hybrid material (i.e. CaF2 and silicon), which is compatible with an ultra-high Q and high thermal conductivity, will allow us to reduce the TOM oscillation and stabilize the optical output.

Evaluation of Polished Surface for Viscoelastic Polymer

Viscoelastic polymers are used as one of coating materials for protecting the products from scratches. Presently, the repair of the coating surface for removing dust or extraneous matters has been performed through several polishing processes. However, it becomes increasingly difficult to polish its surface by only applying good skill and experience of skilled worker because a leading-edge viscoelastic polymer for coating is further scratch-resistant. Thus, based on quantitative evaluation of relation between polishing process and finished surface, it is necessary to make the polishing process appropriate for the leading-edge viscoelastic polymers. In this study, we attempt to establish the evaluation method of the polished surface and clarify the surface condition with invisible scratches.

Sensor-Less Tool Fracture Detection Applying Disturbance Observer Theory

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.

Electrorheological Gel Linear Actuator for Human-Coexistence Robots

Robots manipulated by humans are being aggressively researched and developed. Such robots have requirements such as a large generative force, high-speed response, good controllability, high safety, low friction and backdriveability. We focused on backdriveability and created a prototype for a novel linear actuator with a new structure that includes an electrorheological (ER) gel, which is a recently designed functional material. The device is an all-purpose actuator that satisfies the demands for application in a human-coexistence welfare robot, such as power-assist systems. This paper presents the original plan for the linear actuator, shows the actuator as currently manufactured and presents the basic characteristics of the actuator as investigated experimentally. We obtained larger force from the linear actuator than the initial target. Additionally, the linear actuator shows possibilities of further improvement of the force–weight ratio by an increase of the ER gel structures. With regard to stabilizing the response of the linear actuator, spring elements contributed to its improvement. However, further stabilization remains as a future issue for practical use in human-coexistence robots.

Temperature and shear rate characteristics of electrorheological gel applied to a clutch

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.

Torque sensor-less tactile control of electro-rheological passive actuators

Electro-rheological materials, such as electro-rheological fluid and electro-rheological elastomer, are functional materials which change these viscoelastic properties according to the electrical field intensity. It is expected to apply to the machine element, such as brake and clutch. Meanwhile, sensor-less control system of application devices using ER material is required to cut cost in practical use. In this study, sensor-less viscous torque control of ER passive actuator using parallel disturbance observer (DOB) is proposed. Parallel DOB can estimate the viscous torque from both applied voltage and angular velocity, and realize robust torque control without additional torque sensor. The effectiveness of this method is confirmed from simulation and experiments.

Soliton pulse formation in a calcium fluoride whispering gallery microcavity without frequency sweeping

We study a way of achieving a soliton pulse from a CaF2 microcavity. We fabricated a dispersion controlled CaF2 cavity and also numerically developed a method to generate soliton pulses without sweeping the input laser.