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Energy-Based Control of a Haptic Device Using Brakes
Cho, Changhyun,Song, Jae-Bok,Kim, Munsang IEEE 2007 IEEE Transactions on Cybernetics Vol.37 No.2
<P>This paper proposes an energy-based control method of a haptic device with electric brakes. Unsmooth motion is frequently observed in a haptic system using brakes during a wall-following task. Since it is generally known that a haptic system using brakes is passive due to brake's characteristics, its energy behavior has seldom been investigated. However, force distribution at the end effector reveals that the unsmooth motion of a haptic system using brakes represents active behavior of the system in the specific direction. A force control scheme is proposed that computes the gain for smooth motion by considering the energy behavior of a system. Experiments show that smooth wall following is possible with a proposed force control scheme</P>
Changhyun Cho,Sungchul Kang IEEE 2014 IEEE TRANSACTIONS ON ROBOTICS Vol.30 No.2
<P>We propose a design method for a gravity compensator using unit spring balancers for multi-degree-of-freedom (DOF) and multilink manipulators. Existing spring balancers can be applied to a new design of a gravity compensator. When applying spring balancers to a new gravity compensator, it is necessary to determine how many spring balancers are required and where they should be placed. Our proposed design method can determine the number of spring balancers and their locations. In this study, the design of a spring balancer for multi-DOF and multilink manipulators is considered as a mapping between two spaces (i.e., the joint space for gravitational torques and the spring balancer space to compensate torques). The mapping matrix is obtained through eigenvalue analyses of the potential energy function. The number of rows of the mapping matrix represents the number of unit gravity compensators. The row vector of the mapping matrix also indicates the locations of the unit gravity compensators. Examples are presented to validate the effectiveness of the proposed method.</P>
Changhyun Cho,Seunghun Choi,Oh Min Kwon,Seungha Lee,Jong‑hwan Kim,Dongil Kwon 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.7
Friction stir welding has the advantages of producing less material deformation and of simple joining of relatively thickmaterials, but the disadvantages of forming relatively large heat-affected zones around weld areas. In addition, in research onreductions in bulletproof performance in heat-affected zones, it is necessary to evaluate the ballistic limit velocity (V50), whichmeasures bulletproof performance, and this requires specimens of a certain minimum size and has only limited applicationto local areas such as heat-affected zones. Instrumented indentation testing (IIT), a method of measuring material propertiesby utilizing load-depth curves measured by a small indenter leaving fine marks on the material, has no specimen size requirements;in addition, it has simple test procedures and is nondestructive. Here a theoretical model is proposed for evaluatingV50 of aluminum alloys by ductile hole formation using IIT. Heat-affected zones generated after friction stir welding of for7000-series aluminum alloys were simulated, and the model was validated through comparison with the conventional V50test. In addition, there is currently no way to directly evaluate V50 for welded areas in 7000-series aluminum, but here IIT wasused to assess V50 for each local part of the welded specimen. The conventional V50 test takes 15 min per shot and cannot bereused of specimens, but the test using IIT takes 1 min to complete one test and has benefits in terms of time, cost and safety.
Static balancer for the neck of a face robot
Cho, Changhyun,Kim, Seungjong SAGE Publications 2014 Proceedings of the Institution of Mechanical Engin Vol.228 No.3
<P>We propose a 3-degree of freedom gravity compensator for the neck of a robotic face. The neck of the face robot is configured with yaw-pitch-pitch-roll rotations. Since the yaw rotation is made parallel to gravity, only the pitch-pitch-roll rotations are considered for gravity compensation. The 1-degree of freedom gravity compensator is located at the first pitch joint. A 2-degree of freedom gravity compensator equivalent to the existing gravity compensator is proposed and applied to the second pitch and roll rotations. A parallelogram is adopted between the first and second pitch rotations. One end of the 2-degree of freedom gravity compensator is attached at the parallelogram and the other is fixed at the face. Wires are used to realize a zero-length spring for all gravity compensators and all springs are located at the base for compact design. Experimental results for gravity compensation show that gravitational torques were effectively counterbalanced by the proposed 3-degree of freedom gravity compensator.</P>
Enhanced Degradation of TNT and RDX by Bio-reduced Iron Bearing Soil Minerals
Cho, Changhyun,Bae, Sungjun,Lee, Woojin Techno-Press 2012 Advances in environmental research Vol.1 No.1
We demonstrated that reductive degradation of 2,4,6-Trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (Royal Demolition Explosive, RDX) can be enhanced by bio-reduced iron-bearing soil minerals (IBSMs) using Shewanella putrefaciens CN32 (CN32). The degradation kinetic rate constant of TNT by bio-reduced magnetite was the highest (0.0039 $h^{-1}$), followed by green rust (0.0022 $h^{-1}$), goethite (0.0017 $h^{-1}$), lepidocrocite (0.0016 $h^{-1}$), and hematite (0.0006 $h^{-1}$). The highest rate constant was obtained by bio-reduced lepidocrocite (0.1811 $h^{-1}$) during RDX degradation, followed by magnetite (0.1700 $h^{-1}$), green rust (0.0757 $h^{-1}$), hematite (0.0495 $h^{-1}$), and goethite (0.0394 $h^{-1}$). Significant increase of Fe(II) was observed during the reductive degradation of TNT and RDX by bio-reduced IBSMs. X-ray diffraction and electron microscope analyses were conducted for identification of degradation mechanism of TNT and RDX in this study. 4-amino-dinitrotoluene were detected as products during TNT degradation, while Hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine, Hexahydro-1,3-dinitroso-5-nitro-1,3,5triazine, and Hexahydro-1,3,5-trinitroso-1,3,5-triazine were observed during RDX degradation.