• Journal of Korean Society of Water and Wastewater
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• v.19 no.6
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• pp.767-774
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• 2005

The DOF (Dissolved Ozone Flotation) system was used to treat the effluent of the secondary wastewater treatment plant. The DOF system uses ozone instead of air, while DAF (Dissolved Air Flotation) uses air. Moreover, since the solubility of ozone is higher than air, the DOF system produces larger volume of micro-bubbles than the DAF system does. Thus, the DOF system performs better than the DAF system in floating ability. The DOF system could remove 70% of turbidity to an average of 0.59NTU in effluent from 2.31NTU in influent. The removal efficiency of absorbance measured with UV-254 in the effluent of the DOF system was 63%, while only 19% was removed by the DAF system. the DOF system removed 84% of the color from 25~26CU to 4CU, while DAF system removed 42% of the color to 15 CU. The CODMn removal efficiency of the DOF system was 34%, 6.8mg/l of effluent $COD_{Mn}$ concentratin, while it was 20%, 8.3mg/L of effluent $COD_{Mn}$ concentratin, to use the DAF system. Microbial bacteria such as coliform bacteria, and heterotrophic bacteria were removed over 99% by the DOF system, and 42~45% by the DAF system. That is, Microbial bacteria were almost completely destroyed by the DOF system. To sum up with, the DOF system was found to be very effective to treat effluent of the wastewater treatment plant.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.302-307
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• 2005

Recently, lots of parallel mechanisms for spatial 3-DOF and 6-DOF were investigated. However, research on 4-DOF and 5-DOF parallel mechanisms has been very few. In this paper, we propose a 4-DOF parallel mechanism that consists of 3-rotational and 1-translational motions. The kinematic characteristics of this mechanism are analyzed in terms of an isotropic index and maximum force transmission ratio, and its kinematic optimization is being conducted to ensure enhanced kinematic performances

• Structural Engineering and Mechanics
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• v.21 no.6
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• pp.713-735
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• 2005

Due to the complexity of mathematical expressions, the literature concerning the free vibration analysis of plates carrying multiple three-degree-of-freedom (dof) spring-mass systems is rare. In this paper, the three degrees of freedom (dof's) for a spring-mass system refer to the translational motion of its lumped mass in the vertical ($\bar{z}$) direction and the two pitching motions of its lumped mass about the two horizontal ($\bar{x}$ and $\bar{y}$) axes. The basic concept of this paper is to replace each three-dof spring-mass system by a set of equivalent springs, so that the free vibration characteristics of a rectangular plate carrying any number of three-dof spring-mass systems can be obtained from those of the same plate supported by the same number of sets of equivalent springs. Since the three dof's of the lumped mass for each three-dof spring-mass system are eliminated to yield a set of equivalent springs, the total dof of the entire vibrating system is not affected by the total number of the spring-mass systems attached to the rectangular plate. However, this is not true in the conventional finite element method (FEM), where the total dof of the entire vibrating system increases three if one more three-dof spring-mass system is attached to the rectangular plate. Hence, the computer storage memory required by using the presented equivalent spring method (ESM) is less than that required by the conventional FEM, and the more the total number of the three-dof spring-mass systems attached to the plate, the more the advantage of the ESM. In addition, since manufacturing a spring with the specified stiffness is much easier than making a three-dof spring-mass system with the specified spring constants and mass magnitude, the presented theory of replacing a three-dof spring-mass system by a set of equivalent springs will be also significant from this viewpoint.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.313-318
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• 2001

A haptic hand controller operated by the user's hand can receive information on position and orientation of the hand and display force and moment generated in the virtual environment to the hand. This paper presents a design method for KU-HHC, 6 DOF Korea University-haptic hand controller, which allows separation of workspace from linkage mechanism in consideration of the efficient user operation. First, the 3 DOF mechanism in which all the actuators are mounted on the fixed base is developed by combining a 5-bar linkage and gimbal mechanism. Then, the 6 DOF HHC is designed by connecting the two 3 DOF devices through a handle. This paper presents the forward and inverse kinematics for this device and Jacobian analysis. Improvement of the kinematic characteristics using performance index is also discussed. The hand controller KU-HHC based on this design concept and kinematic analysis was manufactured and shows excellent performance.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.7
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• pp.637-643
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• 2010

The paper is about the development of 6-DOF active vibration isolation systems using VCM. Firstly, formulate the vertical 3-DOF mathematical model under eccentric load, and compare the model with the case in which the center of mass is located at the centroid. And then, complete the 6-DOF mathematical model by formulating the horizontal 3-DOF mathematical model. Find main parameters by comparing the result of the frequency response test with simulation result on the model. Finally, achieve the performance of vibration isolation by applying loop shaping approach & feedforward controller.

• Wind and Structures
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• v.6 no.4
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• pp.291-306
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• 2003

Many investigations have been conducted to find out the reason behind wind-rain-induced cable vibration in cable-stayed bridges. A single-degree-of-freedom (SDOF) analytical model, which could capture main features of wind-rain-induced cable vibration, was recently presented by the writers. This paper extends the SDOF model to a 2DOF model by including the equation of motion of upper rivulet. The interaction between the upper rivulet and the cable is described in terms of nonlinear damping force, linear restoring force, and inertia force. The computed results using the 2DOF model are first compared with the results from simulated wind-rain tunnel tests, and the comparison is found satisfactory in general. The possible mechanisms of wind-rain-induced cable vibration are discussed and a parametric study is then conducted. Finally, the computed results using the 2DOF model are compared with those predicted by the SDOF model. The 2DOF model is found better than the SDOF model but the SDOF model is still acceptable for its simplicity.

• Smart Structures and Systems
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• v.20 no.4
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• pp.397-413
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• 2017

Precast concrete (PC) members are currently being employed for general construction or partial replacement to reduce construction period. As assembly work in PC construction requires connecting PC members accurately, measuring the 6-DOF (degree of freedom) relative displacement is essential. Multiple planar markers and camera-based displacement measurement systems can monitor the 6-DOF relative displacement of PC members. Conventional methods, such as direct linear transformation (DLT) for homography estimation, which are applied to calculate the 6-DOF relative displacement between the camera and marker, have several major problems. One of the problems is that when the marker is partially hidden, the DLT method cannot be applied to calculate the 6-DOF relative displacement. In addition, when the images of markers are blurred, error increases with the DLT method which is employed for its estimation. To solve these problems, a hybrid method, which combines the advantages of the DLT and MCL (Monte Carlo localization) methods, is proposed. The method evaluates the 6-DOF relative displacement more accurately compared to when either the DLT or MCL is used alone. Each subsystem captures an image of a marker and extracts its subpixel coordinates, and then the data are transferred to a main system via a wireless communication network. In the main system, the data from each subsystem are used for 3D visualization. Thereafter, the real-time movements of the PC members are displayed on a tablet PC. To prove the feasibility, the hybrid method is compared with the DLT method and MCL in real experiments.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.4
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• pp.320-328
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• 2007

This paper presents a stiffness modeling of a low-DOF parallel robot, which takes into account of elastic deformations of joints and links, A low-DOF parallel robot is defined as a spatial parallel robot which has less than six degrees of freedom. Differently from serial chains in a full 6-DOF parallel robot, some of those in a low-DOF parallel robot may be subject to constraint forces as well as actuation forces. The reaction forces due to actuations and constraints in each serial chain can be determined by making use of the theory of reciprocal screws. It is shown that the stiffness of an F-DOF parallel robot can be modeled such that the moving platform is supported by 6 springs related to the reciprocal screws of actuations (F) and constraints (6-F). A general $6{\times}6$ stiffness matrix is derived, which is the sum of the stiffness matrices of actuations and constraints, The compliance of each spring can be precisely determined by modeling the compliance of joints and links in a serial chain as follows; a link is modeled as an Euler beam and the compliance matrix of rotational or prismatic joint is modeled as a $6{\times}6$ diagonal matrix, where one diagonal element about the rotation axis or along the sliding direction is infinite. By summing joint and link compliance matrices with respect to a reference frame and applying unit reciprocal screw to the resulting compliance matrix of a serial chain, the compliance of a spring is determined by the resulting infinitesimal displacement. In order to illustrate this methodology, the stiffness of a Tricept parallel robot has been analyzed. Finally, a numerical example of the optimal design to maximize stiffness in a specified box-shape workspace is presented.

• The Journal of Korea Robotics Society
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• v.12 no.1
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• pp.11-18
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• 2017

Static balance of an articulated robot arm at various configurations requires a torque compensating for the gravitational torque of each joint due to the robot mass. Such compensation torque can be provided by a spring-based counterbalance mechanism. However, simple installation of a counterbalance mechanism at each pitch joint does not work because the gravitational torque at each joint is dependent on other joints. In this paper, a 6 DOF industrial robot arm based on the parallelogram for multi-DOF counterbalancing is proposed to cope with this problem. Two passive counterbalance mechanisms are applied to pitch joints, which reduces the required torque at each joint by compensating the gravitational torque. The performance of this mechanism is evaluated experimentally.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.631-637
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• 2005

This paper presents a stiffness analysis method for a low-DOF parallel manipulator, which takes into account of elastic deformations of joints and links. A low-DOF parallel manipulator is defined as a spatial parallel manipulator which has less than six degrees of freedom. Differently from the case of a 6-DOF parallel manipulator, the serial chains in a low-DOF parallel manipulator are subject to constraint forces as well as actuation forces. The reaction forces due to actuations and constraints in each limb can be determined by making use of the theory of reciprocal screws. It is shown that the stiffness model of an F-DOF parallel manipulator consists of F springs related to the reciprocal screws of actuations and 6-F springs related to the reciprocal screws of constraints, which connect the moving platform to the fixed base in parallel. The $6{times}6$ stiffness matrix is derived, which is the sum of the stiffness matrices of actuations and constraints. The six spring constants can be precisely determined by modeling the compliance of joints and links in a serial chain as follows; the link can be considered as an Euler beam and the stiffness matrix of rotational or prismatic joint can be modeled as a $6{times}6$ diagonal matrix, where one diagonal element about the rotation axis or along the sliding direction is zero. By summing the elastic deformations in joints and links, the compliance matrix of a serial chain is obtained. Finally, applying the reciprocal screws to the compliance matrix of a serial chain, the compliance values of springs can be determined. As an example of explaining the procedure, the stiffness of the Tricept parallel manipulator has been analyzed.