Geon Woong Lee

Effect of Carbon Nanotube Pre-treatment on Dispersion and Electrical Properties of Melt Mixed Multi-Walled Carbon Nanotubes / Poly(methyl methacrylate) Composites

Multi-walled carbon nanotubes (MWNTs) pre-treated by concentrated mixed acid or oxidized at high temperature were melt mixed with poly(methyl methacrylate) (PMMA) using a twin screw extruder. The morphologies and electrical properties of the MWNT/PMMA composites were investigated. The thermally treated MWNTs (t-MWNTs) were well dispersed, whereas the acid treated MWNTs (a-MWNTs) were highly entangled, forming large-sized clusters. The resulting electrical properties of the composites were analyzed in terms of the carbon nanotube (CNT) dispersion. The experimental percolation threshold was estimated to be 3 wt% of t-MWNTs, but no percolation occurred at similar concentrations in the a-MWNT composites, due to the poor dispersion in the matrix.

Influence of Silane Coupling Agents on the Interlaminar and Thermal Properties of Woven Glass Fabric/Nylon 6 Composites

In this study, the influence of silane coupling agents, featuring different organo-functional groups on the interlaminar and thermal properties of woven glass fabric-reinforced nylon 6 composites, has been by means of shortbeam shear tests, dynamic mechanical analysis, scanning electron microscopy, and thermogravimetric analysis. The results indicate that the fiber-matrix interfacial characteristics obtained using the different analytical methods agree well with each other. The interlaminar shear strengths (ILSS) of glass fabric/nylon 6 composites sized with various silane coupling agents are significantly improved in comparison with that of the composite sized commercially. ILSS of the composites increases in the order: Z-6076 with chloropropyl groups in the silanes >Z-6030 with methacrylate groups >Z-6020 with diamine groups; this trend is similar to that of results found in an earlier study of interfacial shear strength. The dynamic mechanical properties, the fracture surface observations, and the thermal stability also support the interfacial results. The improvement of the interfacial properties may be ascribed to the different chemical reactivities of the reactive amino end groups of nylon 6 and the organo-functional groups located at the ends of the silane chains, which results from the increased chemical reactivity in order chloropropyl >methacrylate >diamine.

Convolution-Based Trajectory Generation Methods Using Physical System Limits

This paper proposes two novel convolution-based trajectory generation methods using physical system limits such as maximum velocity, maximum acceleration, and maximum jerk. Convolution is a mathematical operation on two functions of an input function and a convoluted function, producing an output function that is typically viewed as a modified version of input function. Time duration parameters of the convoluted functions with a unit area are determined from the given physical system limits. The convolution-based trajectory generation methods to be proposed in this paper have three advantages; first, a continuously differentiable trajectory is simply obtained by applying successive convolution operations; second, a resultant trajectory is always generated satisfying the given physical system limits; third, the suggested methods have low computational burden thanks to recursive form of convolution operation. The suggested methods consider both zero and nonzero initial/terminal conditions. Finally, the effectiveness of the suggested methods is shown through numerical simulations.

Mechanical properties and failure mechanism of the polymer composite with 3-dimensionally stitched woven fabric

The mechanical properties and failure mechanisms of through-the-thickness stitched plain weave glass fabric/polyurethane foam/epoxy composites were studied. Hybrid composites were fabricated using resin infusion process (RIP). Stitched sandwich composite increased drastically the flexural properties as compared with the unstitched fabrics. The breaking of stitching yarns was observed during the flexural test and this failure mode yielded relatively high flexural properties. Composites with stitched sandwich structure improved the mechanical properties with increasing the number of stitching yarns. From this study, it was concluded that proper combination of stitching density and types of stitching fiber is important factor for through-the-thickness stitched composite panels.

Faster and smoother trajectory generation considering physical system limits under discontinuously assigned target angles

This paper suggests a trajectory generation method using convolution operation. The proposed trajectory method always generates differentiable S-curve shape regardless of irregular time intervals, even when a new target is inputted before the trajectory does not reach to the previous target, or when a target is lost due to the communication problems. Also, the proposed method generates a trajectory considering physical system limits, for instance, maximum velocity, acceleration, and jerk, through the successive digital convolution that can reduce computational load, by using a recursive form of convolution operation. The effectiveness of the proposed method is shown through simulations.

Convolution-based Desired Trajectory Generation Method Considering System Specifications

Most motion control systems consist of a desired trajectory generator, a motion controller such as a conventional PID controller, and a plant to be controlled. The desired trajectory generator as well as the motion controller is very important to achieve a good tracking performance. Especially, if the desired trajectory is generated actively utilizing the maximum velocity, acceleration, jerk and snap as given system specifications, the tracking performance would be better. For this, we make use of the properties of convolution operator in order to generate a smooth (S-curve) trajectory satisfying the system specifications. Also, the proposed trajectory generation method is extended to more general cases with arbitrary initial and terminal conditions. In addition, the suggested trajectory generator can be easily realized for real-time implementation. Finally, the effectiveness of the suggested method is shown through numerical simulations.

Transverse Flow and Process Modeling on the Polymer Composite with 3-Dimensionally Stitched Woven Fabric

In resin infusion process(RIP), the fiber and the resin are in contact with each other for an impregnation step and often results in flow-induced defects such as poor fiber wetting and void formation. Resin flow characteristics in transverse direction and process modeling for woven fabric were studied, and the process modeling was applied to the manufacturing of hybrid composite materials. This study also considered the compressibility of woven fabrics in a series of compression force, and it was fitted well to an elastic model equation. Void formation was varied with the processing conditions in the stage of manufacturing composites using RIP. It was concluded from this study that proper combination of pressure build-up and dynamic heating condition makes important factor for flow-induced composite processing.

Trajectory Generation Method with Convolution Operation on Velocity Profile

하지만 로봇에 대한 필요성이 더 이상 산업용 로봇에 국한되지 않고 서비스 로봇 혹은 의료 로봇으로 확대되어 감에 따라 사람과의 공존을 위해 로봇은 외부 환경 인식을 위한 여러 가지 센서로 복잡화 되고 있다. 정해진 궤적을 따라 움직이는 경제성과 효율성이 중요시 되는 산업용 로봇과는 달리 사람과의 공존을 위한 서비스 또는 의료 로 Key Words: Trajectoty Generation(궤적 생성), Convolution Operation(컨볼루션 연산), Real-time Computation(실시간 계산), Kinematic Constraints(운동학적 제약) 초록: 로봇에 대한 필요성이 더 이상 산업용 로봇에 국한되지 않고 서비스 로봇 혹은 의료 로봇으로 확대됨에 따라 사람과의 공존을 위해 외부 환경에 즉각적으로 대응이 가능한 궤적 생성 방법이 요구되고 있다. 이에 본 논문에서는 컨볼루션 연산을 이용한 실시간으로 변경 가능한 궤적 생성 방법을 제시한다. 본 논문에서 제시하는 방법은 기존의 컨볼루션 방법과 같이, 시스템의 운동학적 제약 조건 내에서의 궤적을 생성하며 기존 컨볼루션 방법의 모든 특성을 만족한다. 또한, 항상 사다리꼴 모양으로 궤적이 생성되는 특성으로 인한 특정 상황에서 비효율적으로 궤적이 생성될 수 있는 기존 컨볼루션 방법의 단점을 개선시키는 새로운 방법을 제시한다. 모의 실험을 통해 제안하는 방법의 유효성과 적합성을 보이며, 기존 컨볼루션 방법과의 비교를 통해 그 효율성을 보인다. Abstract: The use of robots is no longer limited to the field of industrial robots and is now expanding into the fields of service and medical robots. In this light, a trajectory generation method that can respond instantaneously to the external environment is strongly required. Toward this end, this study proposes a method that enables a robot to change its trajectory in real-time using a convolution operation. The proposed method generates a trajectory in real time and satisfies the physical limits of the robot system such as acceleration and velocity limit. Moreover, a new way to improve the previous method (11), which generates inefficient trajectories in some cases owing to the characteristics of the trapezoidal shape of trajectories, is proposed by introducing a triangle shape. The validity and effectiveness of the proposed method is shown through a numerical simulation and a comparison with the previous convolution method.