• Journal of Institute of Control, Robotics and Systems
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• v.15 no.1
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• pp.99-104
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• 2009

This article describes the analysis of stable grasping for multi-fingered robot. An analysis method of stable grasping, which is based on the three-dimensional acceleration convex polytope, is proposed. This method is derived from combining dynamic equations governing object motion and robot motion, force relationship and acceleration relationship between robot fingers and object's gravity center through contact condition, and constraint equations for satisfying no-slip conditions at every contact points. After mapping no-slip condition to torque space, we derived intersected region of given torque bounds and the mapped region in torque space so that the intersected region in torque space guarantees no excessive torque as well as no-slip at the contact points. The intersected region in torque space is mapped to an acceleration convex polytope corresponding to the maximum acceleration boundaries which can be exerted by the robot fingers under the given individual bounds of each joints torque and without causing slip at the contacts. As will be shown through the analysis and examples, the stable grasping depends on the joint driving torque limits, the posture and the mass of robot fingers, the configuration and the mass of an object, the grasp position, the friction coefficients between the object surface and finger end-effectors.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.67-70
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• 2004

An investigation was performed to study the impact damage of the laminated composite plates caused by a low- velocity foreign object with multi-scale modeling based on the concepts of Direct Numerical Simulation (DNS)[4]. In the micro-scale part, we discretize the composite plates through separate modeling of fiber and matrix for the local microscopic analysis. A micro-scalemodel was developed for predicting the initiation of the damage and the extent of the final damage as a function of material properties, laminate configuration and the impactor's mass, etc. Anda macro-scale model was developed for description of global dynamic behavior. The connection betweenmicroscopic and macroscopic is implemented by the tied interface constraints of LS-DYNA contact card. A transient dynamic finite element analysis was adopted for calculating the contact force history and the stresses and strains inside the composites during impact resulting from a point-nose impactor. The low-velocity impact events such as contact force, deformation, etc. are simulated in the macroscopic sense and the impact damages, fiber-breakage, matrix cracking and delamination etc. are examined in the microscopic sense.

• Smart Structures and Systems
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• v.17 no.1
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• pp.31-43
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• 2016

Applications of ultrasonic tomography to concrete structures have been reported for many years. However, practical and effective application of this tool for nondestructive assessment of internal concrete condition is hampered by time consuming transducer coupling that limits the amount of ultrasonic data that can be collected. This research aims to deploy recent developments in air-coupled ultrasonic measurements of solids, described in Part 1 of this paper set, to concrete in order to image internal inclusions. Ultrasonic signals are collected from concrete samples using a fully air-coupled (contactless) test configuration. These air coupled data are compared to those collected using partial semi-contact and full-contact test configurations. Two samples are considered: a 150 mm diameter cylinder with an internal circular void and a prism with $300mm{\times}300mm$ square cross-section that contains internal damaged regions and embedded reinforcement. The heterogeneous nature of concrete material structure complicates the application and interpretation of ultrasonic measurements and imaging. Volumetric inclusions within the concrete specimens are identified in the constructed velocity tomograms, but wave scattering at internal interfaces of the concrete disrupts the images. This disruption reduces defect detection accuracy as compared with tomograms built up of data collected from homogeneous solid samples (PVC) that are described in Part 1 of this paper set. Semi-contact measurements provide some improvement in accuracy through higher signal-to-noise ratio while still allowing for reasonably rapid data collection.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.1
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• pp.1-5
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• 2019

The overhead contact line (OCL) is a key piece of equipment for transmitting electrical energy to the pantograph of rail cars. Recently, a 400 km/h OCL was applied to the Honam high-speed line, and its performance was examined by running HEMU-430X. For the study, we analyzed the current of catenary wire concurrently while running HEMU-430X in the Honam high-speed line. Specifically, this study recorded the currents for each speed during operation of the railway vehicle. The analysis of the frequency of line current showed generation of third-harmonics, 15th-harmonics, 17th-harmonics, and 19th-harmonics. The current of catenary wire is a basic technology assessment used to determine the electrical safety of electric railway systems, and it can be used as a technology for analyzing circulating currents generated in the current configuration, as well as for analyzing electric fatigue of the OCL components.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.1564-1567
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• 2008

We demonstrate here a self-aligned printing approach that allows downscaling of printed organic thin-film transistors to channel lengths of 100 - 400 nm. A perfected down-scaled polymer transistors (L= 200 nm) showing high transition frequency over 1.5 Mhz were realized with thin polymer dielectrics, controlling contact resistance, and minimizing overlap capacitance via self-aligned gate configuration.

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.201-202
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• 2007

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.11a
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• pp.301-304
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• 2005

본 논문은 개폐기의 접점 형상에 따른 전계 분포 특성을 2차계 전자계 해석 program인 Flux-2D를 통해 살펴보았다. 2개의 모델을 선정하여 전극간 이격거리를 115[mm], 120[mm], 125[mm]로 변화를 주었을 때 최고 전계 강도의 변화를 살펴보았다. 1000[V] 인가시 최고 전계 강도는 (a)모델에서 115[mm]일 때 61.84[V/m], (b)모델에서 115[mm]일 때 66.90[V/m]로 나타났다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.104-112
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• 2015

Non-contact surface wave transmission (SWT) measurements are used to evaluate the depth of a surface-breaking crack in concrete slabs. The author propose a measurement model that includes an appropriate configuration of the source and receivers, and a transmission function for the given configuration. A series of numerical simulations using a 3D finite element model is used to obtain the transmission function. Then, validity of a proposed model is verified through experimental studies. Two air-coupled sensors are used to measured surface waves across surface-breaking cracks with varying depths from 0mm to 100mm with intervals of 10mm in a concrete slab ($1500{\times}1500{\times}180mm^3$) in laboratory. As a result, the proposed method is demonstrated as to be effective for charactering the depth of a surface-breaking crack in concrete bridge deck with an average error of 10%. A discussion on practical applications of the proposed method is also included in this article.

• Journal of the Korea Computer Graphics Society
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• v.27 no.3
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• pp.13-23
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• 2021

In this paper, we proposed a framework that generates the trajectory of a single rigid body based on its COM configuration and contact pose. Because we use a smaller input dimension than when we use a full body state, we can improve the learning time for reinforcement learning. Even with a 68% reduction in learning time (approximately two hours), the character trained by our network is more robust to external perturbations tolerating an external force of 1500 N which is about 7.5 times larger than the maximum magnitude from a previous approach. For this framework, we use centroidal dynamics to calculate the next configuration of the COM, and use reinforcement learning for obtaining a policy that gives us parameters for controlling the contact positions and forces.

• Journal of Astronomy and Space Sciences
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• v.20 no.4
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• pp.239-248
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• 2003

We completed the light curves of near-contact binary system AX Dra for 11 nights from March 2001 to May using the 61-cm reflector and VR filters at Sobaeksan Optical Astronomy Observatory. From our observations, seven new times of minimum light (three timings to. primary eclipse, four. for. secondary) and the light elements consistent with recent observations were determined. Using the Wilson-Devinney binary code and the q-search method, we analyzed our VR light curves for various Roche configurations and mass ratios. As the results, we found the eclipsing binary AX Dra to be the FO Vir-type near-contact binary system interpreted as a detached or a semi-detached system, with the secondary filling its Roche lobe and the primary almost. Unlike the statistical study(Shaw 1994) of the FO Vir-type near-contact binary system, our VR light curves showed the O'Connell effect of all the same type and it's dimensions was about $0^{m}.008$.