Papers by Author: Chang Doo Kee

Abstract: We report a novel high-performance electroactive polymer actuator based on poly (vinylidene fluoride) (i.e., PVDF) and graphene. The PVDF-graphene composite membranes were fabricated through electrospinning method. The electrospun composite membrane has a three-dimensional network structure, high porosity, and large ionic liquid solution uptake which are a prerequisite for high performance dry-type electroactive soft actuators. The conductive poly (3,4-ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOT:PSS) layers were deposited on the surfaces of the composite membrane through dipping-drying method. The electroactive PVDF-graphene actuators under both harmonic and step electrical inputs show larger bending deformation and faster response time than the pure PVDF actuator. X-ray diffusion (XRD) and ionic conductivity testing results for the PVDF-graphene membrane were compared with those of pristine PVDF. Most important, the PVDF-graphene actuator shows much larger bending deformation under low input voltage, and this could be due to the synergistic effects of the higher ionic conductivity of PVDF-graphene membrane and the electrochemical doping processes of the PEDOT:PSS electrode layers.

Abstract: The residual stress was measured through the proposed method with ESPI measurement system. The proposed measurement method as a basic study combined with theory and experiments applied for residual stresses prediction and developments of safety estimation technique.

Abstract: Fullerene reinforced electrospun cellulose Acetate(CA) nano fibers based composite dry-type actuators were newly developed. Morphology of the electro spun fibers showed good dispersion of the fullerene within the nano fibers whereas XRD studies slight increase in crystallinity. FTIR spectra showed interactions between the hydroxyl moieties of fullerene with cellulose. Stress-strain curves showed substantial increase in tensile strength even with minute concentrations of filler. Our results show nearly three fold increase in tip displacement even with 0.5 wt% fullerenes under both AC and DC conditions. The efficiency of the actuators was also calculated from current-voltage diagrams.

Abstract: In this paper, the visual tracking algorithm for a moving target is proposed for the biped robot of which camera movement is irregular. Hexagonal Matching Algorithm is used to measure the changes of size, location, and rotation angle for a moving object from its image frame. For enhancing the efficiency of the tracking, we can adaptively adjust the starting point and the size of search area from the image information obtained. Finally, by using Affine Transform and Kalman Filter, the position estimation of the moving target is refined against the swing of the camera. Experiments with 20-DOF biped robot using mono vision sensor are implemented to prove the reliability of the proposed method.

Abstract: In this study, an ultrasonic optical fiber hydrogen sensor was newly developed for monitoring and detecting hydrogen leakages. Previously, we developed a pulse-echo sensor system for health monitoring system. Ultrasonic wave, generated from a piezoelectric actuator, is guided and propagated through the optical fiber and subsequently sensed by a piezoelectric sensor in the pulse-echo sensor system. For the detection of hydrogen, the optical fiber was coated with palladium particles, which expanded on exposure to hydrogen. Palladium was used, because it adsorbs hydrogen gas and swell slightly to form palladium hydride with exposure to hydrogen. The change in palladium dimensions affects the wave propagation impedance of optical fiber for detecting the hydrogen gas, and this method has been applied to the pulse-echo sensor systems. Our results showed that the ultrasonic-optical fiber hydrogen sensor can be successfully employed for hydrogen detecting system.

Abstract: In this study, array type fiber-PZT senor systems were newly developed with capabilities of detecting both damage location and monitoring of gas or liquid leakage by applying time-frequency analyses. The system consists of two piezoelectric transducers for the signal receiver and generator applications and three optical fibers for wave propagation. The results showed developed fiber-PZT array sensor can accurately measure the position of crack and its intensity. Also the fluid leakage of methyl alcohol as test specimen, on the plate structure has also been investigated employing the fiber-PZT sensors. The ultrasonic wave optical fiber sensor can be used effectively to monitor changes in structural and chemical properties.

Abstract: To measure the micro-mechanical properties for micro/nano materials, out-of-plane ESPI system and micro-strip bend testing system were developed. For the bending system, PZT actuator was controlled with the stroke resolution of 0.6 nm and out-of-plane ESPI system was developed in compact and portable type. To quantitatively analyze the out-of-plane ESPI fringe patterns, 4-bucket technique was used and unwrapped phase map was obtained. Electrolytic copper foil with the thickness of 18 μm was used for preparation of the strip bend specimen with length of 8 mm and three different widths of 2, 3 and 5 mm. The strip bending tests showed that the out-of-plane deflection in the bend specimen was measured with a maximum of 8 % in error. Furthermore, from the experiment, the variation of the deflection along the supporting span could be determined and significant region was linear.

Abstract: To determine the micro-mechanical properties for micro/nano materials, it may be essential to measure the strain/deformation during micro-mechanical testing. Therefore, in this study, continuous measurement of in-plane tensile strain in micro-sized specimens of thin film materials was introduced using the micro-ESPI technique. TiN and Au thin films 1 and 0.47µm thick, respectively, were deposited on the silicon wafer and fabricated into the micro-sized tensile specimens by the electromachining process. The micro-tensile loading system and micro-ESPI system were developed to measure the tensile strain during micro-tensile loading. Micro-tensile stress-strain curves for these materials were determined using the algorithm for continuous strain measurement. Furthermore, the new algorithm for enhancing the sensitivity to measurement of in-plane tensile strain was suggested. Using the algorithm, micro-tensile strain data between interfringes were calculated. It is shown that the algorithm for enhancement of the sensitivity suggested in this study makes the sensitivity to the in-plane tensile strain increase.