Jong-Won Lee

(Mn,Cu) 3 O 4 -based conductive coatings as effective barriers to high-temperature oxidation of metallic interconnects for solid oxide fuel cells

Abstract(Mn,Cu)3O4-based conductive oxides are examined as protective coatings to improve the surface stability of metallic interconnects for solid oxide fuel cells at high temperatures. Nano-sized Mn3u2009−u2009xCuxO4 materials with various Cu contents (xu2009=u20091.0–1.5) are synthesized and a composition-structure–property relationship is experimentally determined. The Cu content (x) has a significant influence on phase stability as well as sintering, electrical, and thermal expansion characteristics. Thin and dense Mn3u2009−u2009xCuxO4 coatings are fabricated on the interconnects (Crofer 22 APU) by a slurry coating process and subsequent heat treatment. The coated interconnects exhibit area-specific resistances as low as 7.1–15.0xa0mΩxa0cm2 at 800xa0°C. The electrochemical cell shows no performance degradation in the presence of the Mn3u2009−u2009xCuxO4-coated interconnect. The results indicate that the Mn3u2009−u2009xCuxO4 coatings act as an effective barrier to high-temperature oxidation of the metallic interconnects.

Development of novel LSM/GDC composite and electrochemical characterization of LSM/GDC based cathode-supported direct carbon fuel cells

Abstract(La0.8Sr0.2)0.95MnO3−δ (LSM)–Gd0.1Ce0.9O2−δ (gadolinium-doped ceria, GDC) composite cathode material was developed and characterized in terms of chemical stability, sintering behaviour, electrical conductivity, mechanical strength and microstructures to assess its feasibility as cathode support applications in cathode-supported fuel cell configurations. The sintering inhibition effect of LSM, in the presence of GDC, was observed and clearly demonstrated. The mechanical characterization of developed composites revealed that fracture behaviour is directly affected by pore size distribution. The Weibull strength distribution showed that for bimodal pore size distribution, two different fracture rates were present. Furthermore, the contiguity of LSM and GDC grains was calculated with image analysis, and correlation of microstructural features with mechanical and electrical properties was established. Subsequently, an LSM/GDC-based cathode-supported direct carbon fuel cell (DCFC) with Ni/ScSZ (scandia-stabilised zirconia) anode was successfully fabricated via slurry coating and co-firing techniques. The microstructures of electrodes and electrolyte layers were observed to confirm the desired morphology after co-sintering, and a single cell was electrochemically characterized in solid oxide fuel cell (SOFC) and DCFC mode with ambient air as oxidant. The higher values of open-circuit voltage indicated that the electrolyte layer prepared by vacuum slurry coating is dense enough. The corresponding peak power densities at 850xa0°C were 450 and 225xa0mWxa0cm−2 in SOFC and DCFC mode, respectively. Electrochemical impedance spectroscopy was carried out to observe electrode polarization and ohmic resistance.

Method for improving the position precision of a hydraulic robot arm: dual virtual spring---damper controller

Recently, control approaches for a hydraulic robot in the field of robotics have attracted considerable attention owing to their high power-to-weight ratio. Many studies on behavior and control exploiting the advantages of hydraulic robots have been pursued. Application to hydraulically actuated systems, however, is not straightforward due to the nonlinear internal dynamics of the actuators. This paper presents a relatively simple method to improve the position precision of a hydraulic robot arm. We propose a simple control method concept based on a virtual spring–damper (VSD) controller, which enables the robot to realize a desired position. The main advantage of the VSD control is its simple calculation method, which eliminates the need to solve the Jacobian pseudo-inverse or ill-posed inverse kinematics. In this study, experiments were conducted to identify the problems in previous study results and evaluated the applicability of VSD control to the hydraulic robot arm. A relatively simple method was proposed to solve these problems and to verify improvements in the position precision. The proposed method is the dual VSD controller in which an additional VSD model is applied to the elbow, in addition to the conventional VSD model connected to the wrist. The effectiveness of the proposed control scheme is demonstrated in experimentation with the hydraulic robot arm.

A simulation study on the control of lower extremity exoskeleton for assistance of human locomotion

The best feature of the exoskeleton system is a symbiotic relationship between the wearer and the exoskeleton. To form perfect symbiotic relationship, the exoskeleton should exactly detect wearers intention to move. Earlier studies have proposed a variety of methods to detect the wearers intention and control methods using them. However, existing methods are highly dependent on the additional sensor systems and precise dynamic models. In this paper, we propose a novel control method of lower extremity exoskeleton for assistance of human locomotion. The control method is motivated by examining the human locomotion. To verify the effectiveness of the proposed method, we develop a simple mathematical model to simulate the stance phase of human locomotion and conduct the simulation. Our preliminary study shows that the proposed control method can effectively decrease the net external mechanical work performed by legs.

Virtual model control of lower extremity exoskeleton for load carriage inspired by human behavior

The most significant feature of the exoskeleton system, which distinguishes it from other robotic systems, is the symbiotic relationship between the exoskeleton and the wearer. For perfect symbiotic relationship, the exoskeleton should be able to exactly detect the wearer’s intention to move. Existing methods by which lower extremity exoskeletons can detect human intentions are highly dependent on additional sensor systems or accurate dynamic models. In this paper, we propose a novel method for detecting human intention inspired by human behavior, and a control method that utilizes it. We define human intention as the tendency of humans to maintain a statically stable posture and minimize joint torques when supporting payloads. The control method reduces the computational requirements and simplifies the exoskeleton sensor system compared to existing methods. The experimentally measured ground reaction force was used to indirectly estimate the effects of our method on the wearer. The results suggest that the proposed method reduces the load acting on the wearer during locomotion under loaded conditions, and results in a portion of his body weight being supported by the exoskeleton when he is in an uncomfortable position.